A control device of an internal combustion engine is provided. In the case where a switch request for switching from all-cylinder operation to partial-cylinder operation is made, before a switch from the all-cylinder operation to the partial-cylinder operation is executed, an intake air amount increase control increasing an intake air flow rate of an engine by increasing an opening degree of a throttle valve is performed, an ignition timing retardation control retarding an ignition timing is performed, and based on a retardation limit value of the ignition timing at a time point when the switch request is made, a start timing of the intake air amount increase control is changed. As a retardable amount being a difference between an initial ignition timing and the retardation limit value decreases, the start timing of the intake air amount increase control is delayed further.