A particulate filter (41) which traps particulate matter in the exhaust gas of a diesel engine (1), regenerates when a controller (31) performs an exhaust gas increase operation which includes decreasing the opening of an intake throttle (42). The controller (31), during regeneration of the filter (41), determines whether or not the required load of the diesel engine (1) is increasing from an accelerator pedal depression sensor (32) or a fuel injection amount (S3), and prevents output decrease of the diesel engine (1) by interrupting the exhaust gas temperature increase operation when the required load is increasing (S5).