An injection molding apparatus capable of minimizing cracks at the corners of a mold is provided. The playing piece has a memory for storing data and is arranged to derive a power supply from the signal supplied by the game module by coupling to a user so as to complete an electrical path via the user back to the game module and to communicate data with the game module when power is thereby derived by the power deriving means from the signal provided by the game module. Each short-circuit member includes an annular base portion and three arms radially extending from the base portion. And the negative electrode active material contains at least one element selected from the group consisting of Al, Si, Ge, Sn, P, Sb and Bi and has at least one crystal structure selected from the group consisting of BiF3 structure, Cu2MnAl structure, and AgAsMg structure.