A fuel tank includes a tank main body having an opening, a pump unit mounted to a mounting position on a bottom of the tank main body through the opening and having a fuel pump and a pump retaining member retaining the fuel pump and, and a guide means configured to guide the pump unit from an opening side of the tank main body to the mounting position on a bottom side of the tank main body. The guide means includes a guide rail provided on the tank main body and a slider provided on the pump unit. The slider is configured to be slidably engaged with the guide rail.