フローチャートの作り方 完全ガイド

Standard flowchart symbols and when to use them

Four shapes cover 90% of flowcharts. The rectangle (process box) represents an action or step: 'Send confirmation email'. The diamond represents a decision with two or more outputs: 'Payment successful? → Yes / No'. The oval (terminator) marks the start and end of a process. The parallelogram represents input or output: 'User enters card number'.

For more complex diagrams, use the cylinder for database storage, the document shape for outputs like reports or logs, and the trapezoid for manual operations. Consistent use of these shapes — rather than using rectangles for everything — makes your flowchart readable by anyone familiar with the notation.

Arrows should flow in one direction as much as possible (usually top-to-bottom or left-to-right). Crossing arrows are a sign that the process itself may need rethinking. If you have more than three crossings, consider breaking the flowchart into sub-diagrams with reference links.

When to use a flowchart vs. other diagram types

Use a flowchart when you're documenting a sequential process with decision points — user registration, a refund workflow, or a bug triage process. Flowcharts excel at showing the 'happy path' plus error branches in a single view.

Use a swimlane diagram instead when multiple people, teams, or systems share responsibility for different steps of the same process. Swimlanes make handoffs explicit. Use a sequence diagram when the timing and order of messages between systems matters — API calls, OAuth flows, and event-driven architectures are better modeled as sequence diagrams.

Use a state diagram when you're modeling the lifecycle of an object (order status, payment state, subscription tier). Each node is a state, not a step — the difference matters when an object can re-enter a state or transition in multiple directions.

Flowchart best practices

Start with the happy path — the sequence of steps that happens when everything goes right. Add decision branches for errors and exceptions only after the main flow is clear. This makes the diagram readable regardless of how familiar the reader is with edge cases.

Label every arrow from a decision diamond. A diamond with an unlabeled 'Yes' branch and an unlabeled 'No' branch forces the reader to guess which is which. Label with 'Yes', 'No', 'Success', 'Failure', 'Approved', or whatever makes the branch condition explicit.

Keep each box to one action. 'Validate email, check password, and log the attempt' should be three boxes, not one. Single-responsibility boxes make it easier to add error handling later and keep the diagram scannable.

Generate a flowchart from text with AI

Describe your process in plain English — 'Signup, email verification, profile setup, optional team invite, end at the dashboard — happy path and error branches' — and AIDrawIO generates a complete flowchart with the correct shapes, decision diamonds, and labeled arrows.

The output is draw.io XML. You can copy it directly into diagrams.net, draw.io desktop, or import it into Confluence. Sign up to export as SVG or PNG for presentations.