A control device of a diesel engine is provided. The device includes an engine body having a cylinder, a fuel injection valve for injecting fuel into the cylinder, a valve timing control module for changing opening and closing timings of at least an intake valve or an exhaust valve, an oxidation catalyst arranged within an exhaust passage for purifying HC discharged from the cylinder, and a DPF arranged downstream of the oxidation catalyst for capturing soot within exhaust gas. The device also includes a DPF regenerating module for supplying, when a predetermined DPF regeneration condition is satisfied, HC to the oxidation catalyst to regenerate the DPF by heat generated from an oxidation reaction of HC, and a fuel cutting module for stopping, when the diesel engine is in a deceleration state, a main injection of the fuel that is performed on a compression stroke of the cylinder.