A reel of a recording tape cartridge includes a reel hub formed in a bottomed cylindrical shape, an annular reel gear coaxially disposed at an outer surface of a bottom portion of the reel hub, and a through-hole the penetrates the axial center of the bottom portion and opens to an outer surface side of the bottom portion. The reel is resin-molded using a mold comprising a fixed mold, a movable mold and an insert. The reel gear and the through-hole are formed by a reel gear forming portion and a hole portion forming portion disposed in a single insert. As a result, the axial centers thereof are aligned with high precision.