Rough road determination device

A rough road determination method for a vehicle, the vehicle having an internal combustion engine, a crank angle sensor that is installed in the internal combustion engine and an ECU, the rough road determination method comprising:

• calculating a first amplitude fluctuation amount by the ECU, the first amplitude fluctuation amount being an amplitude fluctuation amount of one wise of an output of the crank angle sensor;
• calculating a second amplitude fluctuation amount by the ECU, the second amplitude fluctuation amount being an amplitude fluctuation amount of one pulse that is actually output from the crank angle sensor and being determined in advance on a basis of a rotational speed of the internal combustion engine;
• determining by the ECU whether or not a road on which the vehicle travels is a rough road, by comparing the first amplitude fluctuation amount with the second amplitude fluctuation amount in order to control with the ECU an ignition timing of the internal combustion engine according to the rough road determination.