An injection molding apparatus includes a first mold and a second mold, a cavity formed by clamping the first mold and the second mold, and includes a portion where the ratio of a first dimension and a second dimension changes continuously such that a portion where the ratio of the first dimension of a pair of first surfaces, and the second dimension of a pair of second surfaces becomes 1 locates in an intermediate portion of the cavity in a longitudinal direction of the long shape; and a first temperature adjusting circuit that is provided at the first mold and the second mold to adjust a temperature within a range where the second dimension of the second surfaces is greater than the first dimension of the first surfaces such that the temperature of the pair of first surfaces becomes higher than the temperature of the pair of second surfaces.