A blockage detection device opens a purge valve in a state where a negative pressure pump is operated. The negative pressure pump is connected to a downstream side of a canister with respect to a fuel tank, and reduces pressure in a device internal space. The blockage detection device calculates gas information (volume V, for example) of the device internal space on the basis of variation of internal pressure before and after the purge valve is opened. The blockage detection device detects a blockage in a vent line using the calculated gas information.