In a printer including a reflection type optical sensor and a transmission type optical sensor arranged to oppose each other across a paper conveyance path, a sensor spring and a plate spring are elastically deformed consequent to the wave shape of a guide unit and a guide unit, according to the positions of the reflection type optical sensor and the transmission type optical sensor along the width direction of the printer, enabling the reflection type optical sensor and the transmission type optical sensor to be moved based on the pitch of the wave shape along the width direction of the printer while transmitting a click feeling to an operator each time the sensor spring and the plate spring climb over a protruding portion of the wave shape.