An irradiation device of a lamination molding apparatus includes: at least one laser source, generating a laser beam; a first galvano scanner, scanning the laser beam; a second galvano scanner, scanning the laser beam; and an irradiation controller, controlling the laser source, the first galvano scanner, and the second galvano scanner. Irradiable ranges of the laser beams by using the first galvano scanner and the second galvano scanner respectively include an entire of a molding region. A first X-axis galvano mirror and a first Y-axis galvano mirror of the first galvano scanner and a second X-axis galvano mirror and a second Y-axis galvano mirror of the second galvano scanner are disposed to be plane-symmetric to each other.