To provide a primer composition adhesive to concrete bed or hardened concrete surface, being such that: a construction product layered with a coating material is hardly peeled.

The primer composition is a solvent-type epoxy resin primer composition comprising an epoxy resin principal ingredient and a curing agent, being such as to contain a methyl methacrylate-butadiene-styrene copolymer resin, wherein the copolymer resin is such that: methyl methacrylate is graft-polymerized, with a styrene-butadiene rubber as the core, to be made to the shell, and to be swelled with an epoxy resin. As to this primer composition, a coated floor to be layered is an epoxy resin-coated floor.