A flush toilet includes a reservoir tank assembled from above or behind to a predetermined installation position on the rear side of the conduit of a toilet main unit; a connecting pipe member, one end of which is disposed on the conduit of the toilet main unit, and the other end of which is connected to a reservoir tank; a tank-side connecting portion, disposed on the front side of the reservoir tank and connected to a connecting pipe member; and a seal member, connected in a watertight manner between a connecting pipe member and a tank-side connecting portion.