PURPOSE: To detect an omitted letter for sure in a printing device that uses a hammer by constituting the hammer partially with a magnetized body which comprises a non-magnetic section and providing a magnetic head that corresponds to the non-magnetic section and detecting the movement of the hammer.

CONSTITUTION: In a impact printer in which the type of a printing mechanism 7 is pushed out to print by driving a hammer 14, the hammer 14 is formed with a magnetic body and a notch 15 is provided in a part of the magnetic body and a magnetic head 16 is provided that corresponds to the notch 15. When with this arrangement a coil 18 is magnetized by a drive signal DV and the hammer 14 is moved through an actuator 17, and the printing mechanism 7 is pushed and made to strike to print, the magnetic head 16 changes from the state that a magnetic circuit 21 is formed to the state that the magnetic circuit 21 is not formed. Accordingly by comparing a signal for this change with a driving signal of the hammer 14, it can be detected whether or not there is movement of the hammer 14.