Mold device and method for manufacturing resin molded article

A mold device that forms a cavity for molding a resin molded article including a main body portion and an undercut portion, the mold device comprising:

• a mold main body that molds the main body portion;
• a rotary core that molds the undercut portion and is released from the undercut portion by rotating in a direction in which the rotary core moves away from the undercut portion;
• a regulating core that regulates a rotation of the rotary core by entering between the mold main body and the rotary core and supporting the rotary core at a time of molding, moves away from between the mold main body and the rotary core when the rotary core is released from the undercut portion, and is apart from the mold main body and the rotary core;
• a shaft member that pivotally supports the rotary core on the mold main body and serves as a center of rotation of the rotary core;
• a rotary driving unit that rotates the rotary core using the shaft member as the center of rotation by providing a rotary driving force to the rotary core;
• and
• a lowering cylinder that moves the regulating core;
• wherein as a result of transmission of the rotary driving force from the rotary driving unit, the rotary core rotates independently of a movement of the regulating core, and
• the rotary driving unit provides, at a time of molding, the rotary core with the rotary driving force directed toward the cavity.