A base member includes a lead frame and a resin molded body in which the lead frame is embedded. The resin molded body and the lead frame define a plurality of recesses arranged in a matrix along a first direction and a second direction orthogonally crossing the first direction in a plan view. The resin molded body has a plurality of bottom surface portions each defining a part of a bottom surface of a corresponding one of the recesses, and a wall portion surrounding each of the bottom surface portions in the plan view, with an upper surface of the wall portion defining at least one a groove portion extending in the first direction or the second direction.