To accurately perform control of ignition timing without a great increase in cost in remodeling of a gasoline engine to a gasoline alternate fuel engine.

In the ignition control method to be executed in a gasoline alternate fuel injection system including a non-gasoline fuel electronic control unit 3A added to an existing gasoline injection system of an engine 1, the unit 3 receiving a gasoline injection signal B output from a gasoline electronic control unit 2 according to a detected engine operating state, calculating an injection quantity of non-gasoline fuel based thereon and outputting an injector drive signal K to an injector 4, the non-gasoline fuel electronic control unit 3A receives a crank angle signal P output from a crank angle sensor 7 as an engine rotation signal detection means, and generates/outputs an ignition signal R suitable to non-gasoline fuel based thereon to directly control an ignition coil device 6.

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