A reliable and superior joining strength in entire joining parts of resin molded bodies including tilting portions is obtained by devising a shape and a size of each protrusion for welding provided in the joining parts of the resin molded bodies. The joining parts of upper and lower half bodies 10 and 20 have vertical portions 11 and 13 and vertical portions 21 and 23 respectively vertical to a pressurizing direction and tilting portions 12 and 22 tilting relative to the pressurizing direction, and protrusions for welding 11E to 13E or 21E to 23E are provided in at least the joining part of one of the half bodies. Further, referring to a butting area of the protrusions in a butted state, the butting area in the vertical portions is set to be less than the butting area in the tilting portions.