When it is determined that there is a possibility of start-up of an internal combustion engine (11) while regeneration control is in execution during stop of the internal combustion engine (11), processing of the regeneration control is stopped. Accordingly, as compared with the case where the regeneration control is continuously executed when the internal combustion engine (11) is started up, temperature increase in a filter (13) can be suppressed. Therefore, even when an increased amount of oxygen is supplied to the filter, an oxidation reaction is suppressed, so that overheating of the filter (13) can be suppressed.