To provide an optical scanning device and an image forming device capable of detecting occurrence of writing position deviation, and performing alignment correction, based on the detection result.

When a control part starts image forming processing (S102) by receiving print instruction (S101), a pulse width is measured by a pulse-width measuring means (S103), and the number of clocks having the pulse width is detected, and it is determined, based thereon whether mutual position deviation of laser light occurs or not (S104). When determined that position deviation occurs, its information is preserved in a storage part (S105); and when determined that position deviation does not occur, return to step 103 is made. When the instructed print is finished (S106), the information preserved in the storage part is read, and it is determined whether correction is necessary or not (S107), and if correction is necessary, transfer to alignment correction is performed (S108), and if not, a series of processing is finished.