A leak check apparatus performs a leak check of a fuel vapor processing apparatus based on a change in a negative pressure in a purge line during leak down. The pressure change during leak down is corrected by measuring an amount of vapor generated after the purge line is opened to the atmosphere. A first pressure change rate of the purge line is measured after a predetermined negative pressure is applied to the purge line, and the purge line is sealed at the negative pressure. A second pressure change rate of the purge line is measured after the first pressure change rate of the purge line is measured, the cut valve is opened to expose the purge line to the atmosphere, and the purge valve and the cut valve are closed to seal the purge line at the atmospheric pressure. The second pressure change rate measurement does not begin until the degree of pressure increase in the purge line exceeds a predetermined reference value.