Provided is an image forming device (1) that performs additional printing, including: an image forming unit (11) that prints an additional image on a transfer medium; a storage (115,119) that stores information about an alignment image printed on the transfer medium; a reader unit (20) that reads the alignment image printed on the transfer medium on an upstream side of the image forming unit (11) along the transfer direction of the transfer medium; and a control unit(100) that detects and distinguishes multiple alignment images upon reception of reading results from the reader unit(20). The control unit (100) performs control of storing adjustment information for adjusting the position of the additional image to be formed, according to multiple alignment images, in the storage (115,119).