The purpose of the present invention is to provide a handle body for a toothbrush, the handle body having sufficient strength even if subjected to a load in normal use. A handle body for a toothbrush comprises: a handle section (20); and a head section (10) having a bristle embedding surface (11) on one side of the head section (10) in the thickness direction and provided at the front end of the handle section. The handle body also comprises: a first member (4) formed from a first resin; and a second member (6) formed from a second resin which has higher strength than the first resin and joined to the first member in the longitudinal direction of the handle body (2). The first member has at least a part of the handle section, and the second member has the head section and an extension section (40) which extends from the head section toward the handle section. The extension section has a core section (41) protruding toward the handle section from a joint (9) where the first member and the second member are joined. The surface (41a) of the core section, which is located on the other side in the thickness direction, and the joint are connected by a curved surface (42) recessed toward the intersection between the joint and the surface on the other side.