To obtain a temperature required for forced regeneration processing of a DPF.

When forced regeneration processing of the DPF is executed during stopping of a vehicle, the idle rotation speed of a diesel engine is increased to a prescribed rotation speed (S11) and an instruction opening degree θ to a variable turbocharger is set to an initial opening degree (S12). Then, a control signal corresponding to the instruction opening degree θ is output to the variable turbocharger to control the opening degree (S18) while the instruction opening degree θ is increased and decreased within a range demarcated by a lower limit opening degree and an upper limit opening degree (S13 to S17) so that the temperature T of exhaust flowing in the DPF approaches a prescribed temperature. When the temperature T of the exhaust does not approach the prescribed temperature even though the instruction opening degree θ is increased and decreased to the lower limit opening degree or the upper limit opening degree, it is determined that failure is caused in the variable turbocharger and a warning light is lit (S23 and S24).