A preparation control for suppressing fluctuation of an output torque of the engine at the time of executing switching operation from the whole cylinder operation to the partial cylinder operation is executed when having made a switching request from the whole cylinder operation to the partial cylinder operation, the valve operation phase is fixed to a predetermined phase before executing the switching operation, and the cylinder deactivation mechanism is controlled so as to execute the switching operation at a target switching time which is prefixed by corresponding to the predetermined phase. The target switching time is previously set to a timing at which abnormal noises are not generated, by corresponding to the valve operation phase fixed to the predetermined phase.