Provided is a control device for an engine comprising an engine whose combustion mode is switchable according to an engine operation state, wherein the control device is capable of controlling the engine while suppressing generation of knock noise due to abnormal combustion. The control device comprises: a basic target torque-determining part (61) configured to determine a basic target torque based on a vehicle driving state including manipulation of an accelerator pedal; a torque reduction amount-determining part (63) configured to determine a torque reduction amount based on a vehicle driving state other than the manipulation of the accelerator pedal; a final target torque-determining part (65) configured to determine a final target torque based on the basic target torque and the torque reduction amount; and an engine control part (69) configured to set the combustion mode to a premixed combustion mode or a diffusion combustion mode according to the engine operation state. The engine control part is configured, when the engine operation state changes from a diffusion combustion region to a premixed combustion region, due to a change in the final target torque corresponding to a change in the torque reduction amount, to maintain the combustion mode in the diffusion combustion mode.