To provide a control device for a diesel engine capable of certainly suppressing the generation of HC in a transient state.

The control device for the diesel engine 1 provided with an EGR device 2 for recirculating a part of exhaust gas to an intake system includes a glow plug 16 and a control unit 9. The glow plug 16 is arranged in the cylinder of the diesel engine 1 and develops heat in an energized state. The control unit 9 determines whether the operating state of the diesel engine 1 is a transient state. When the control unit determines that the operating state is the transient state, the glow plug 16 is set to an energized state.