OCCLUSION DIAGNOSIS DEVICE

Occlusion diagnosis of a vent passage is executed with high accuracy based on an estimated value of the volume of a sealed space. An occlusion diagnosis device includes a diagnosis unit for the diagnosis. An occlusion diagnosis unit of the diagnosis unit executes the occlusion diagnosis, based on whether or not an estimated volume of a sealed space of a fuel-vapor sealing system exceeds a volume threshold. The occlusion diagnosis determines that the vent passage is suspected of being occluded if the estimated volume is equal to or less than the volume threshold, while diagnoses that the vent passage is not occluded if the estimated volume exceeds the volume threshold. If it is determined that the vent passage is suspected of being occluded, the occlusion diagnosis unit suspends the occlusion diagnosis of the vent passage until a cumulative exhaust amount of fluid at least exceeds an exhaust amount threshold.