A hybrid control method controls a hybrid vehicle. A control unit sets a rotational speed threshold value at which a continuous gear tooth striking sound occurring in a gear mechanism connecting an electric power generation motor to the internal combustion engine is not a problem in terms of vehicle quality. The control unit generates negative pressure while maintaining the engine rotational speed in the firing state where the engine rotational speed is equal to or greater than the rotational speed threshold value. Also, the control unit generates negative pressure after switching from the firing state to a motoring state where the internal combustion engine is rotated by the electric power generation motor and where the engine rotational speed is less than the rotational speed threshold value.