PURPOSE: To increase the cross-sectional area of a gate part, thereby prevent troubles such as a jetting phenomenon and contrive higher productivity, by providing an injection gate extending in a circumferential direction at a position corresponding to an inner peripheral surface of a hole to be formed by molding.

CONSTITUTION: An upper half 10 of a tape cassette casing is provided with a pair of left and right reel shaft-inserting holes 11. For example, an annular gate 12 is provided at a position corresponding to the inner peripheral surface of the inserting hold 11, and a resin is injected the gate 12 to mold the half 10. The gate 12 is so provided as to communicate with a runner 13 left after molding, and is disposed at the position corresponding to the inner peripheral surface of the inserting hole 11. A molten resin injected through the gate 12 flows to the entire part of the half 10. With this construction, the period of time required for the resin to fill a cavity 23 can be shortened by increasing the cross-sectional area of the gate 12. In addition, a jetting phenomenon is prevented from occurring, a pressure loss at the gate part 12 is made to be extremely small, and molding at a low injection pressure enables the use of a large-diameter screw.