The present invention relates to a spring member mounting structure, which is a structure for mounting a spring member on a cushion frame connecting side frames by use of a rear pipe. The spring member has rear clipping portions engaged with the rear pipe. Cover members, which are provided at seat central sides of connecting portions of the side frames and the rear pipe, have extension portions extending toward the seat central sides. The rear clipping portions abut on ends of the seat central sides of the extension portions, and are mounted to the rear pipe by width direction positioning of the spring member.