The present invention accurately detects the state of a radiated light beam. According to the present invention, a calibration unit for a metal 3D printer that radiates a light beam at a powder to mold a built part has: a base part that is attached to a stage that is irradiated with the light beam from the metal 3D printer; and a plurality of attachment parts that are provided to the base part at different locations and have detection devices that detect the light beam attached thereto. The attachment parts are provided at different angles such that the detection directions of the detection devices attached thereto are different.