An ECU drives a pump in a first stage at a first pumping capacity. The ECU drives the pump in a second stage after the first stage at a second pumping capacity, which is lower than the first pumping capacity. The second pumping capacity is set such that when at least one leak hole, which forms a predetermined total opening cross sectional area, exists in the purge apparatus, the driving of the pump at the second pumping capacity substantially maintains a predetermined reference pressure in the purge apparatus. The ECU diagnoses whether a leak hole exits in the purge apparatus based on the pressure measured with the pressure sensor in view of the predetermined reference pressure at the time of driving the pump in the second stage at the second pumping capacity.