A terminal box of solar cell module, comprising a box main body consisting of a resin molding, provided with a bottom plate, an outside plate erected at a peripheral area of the bottom plate and an inside plate defining a circuit storage area for storage of electrical circuits, erected inside the outside plate; an electric circuit housed in the circuit storage area; a filler filling the circuit storage area; an inside cover consisting of a metal plate formed into a lid, provided with a top plate and a side plate suspended from the periphery of the top plate, which inside cover is externally fitted to the inside plate of the box main body to thereby cover the circuit storage area; and an outside cover adapted to engage with the outside plate of the box main body and cover the inside cover and the box main body, which terminal box is fitted with an engaging part capable of causing the inside cover to engage with the box main body to thereby prevent floating of the inside cover from the circuit storage area.