Injection molding apparatus and injection molding method

A space is formed at a tip portion of a nozzle so as to decrease a thermal transfer of the nozzle . Alternatively, a center portion of one of a semi-spherically protruded surface of the tip portion of the nozzle and a semi-spherically recessed surface of a sprue bush protrudes so that the radius of curvature of one semi-spherical surface is the same as the radius of curvature of the other semi-spherical surface. As a result, since the nozzle and the sprue bush are surface-contacted, heat of the tip portion of the nozzle absorbed to the sprue bush is increased. Thus, the temperature of the tip portion of the nozzle can be lowered easily. After the resin material injected into the molding cavity is cooled, when the sprue portion is removed from the fixed die, a tip portion of a rod-shaped protrusion portion of the sprue can be properly cut.