PURPOSE: To prevent detection accuracy from being lowered due to an ink mist adhered to a head or the like, by a construction wherein movement of a belt fixed to a head carriage is detected through the number of pulses generated by a rotary encoder.

CONSTITUTION: The head carriage 15 is fixed to the belt 13, and the belt 13 is driven by rotating a motor 11, thereby reciprocating the carriage. The movement of the belt is detected through the number of pulses generated by the rotary encoder 16. The encoder 16 is of the hermitically sealed type, so that the detection accuracy is not lowered even in the presence of an ink mist, and minute movements can be detected by enhancing the resolving power.