Provided is a spacer configured such that a protruding portion remaining after removal of a portion unnecessary after molding does not contact an inner wall of a coolant water flow path and therefore, even a portion of the spacer in the vicinity of the remaining portion can be positioned close to the cylinder bore side inner wall. The spacer of this embodiment is a spacer (4) formed of a resin molded body and inserted, in use, into a coolant water flow path (3) through an opening (30) of the coolant water flow path (3) that is formed around a plurality of cylinder bores (2) formed adjacent to each other in a cylinder block (1) of an internal combustion engine. The spacer (4) includes a spacer body (40) formed in a cylindrical shape to surround the cylinder bores (2), and a protruding remaining portion (5) remaining after removal of a portion (6ba) necessary in molding and unnecessary after molding. The remaining portion (5) is formed at an end surface (44a) positioned on a side close to the opening (30) of the spacer body (40).