Abstract: A data transfer apparatus is disclosed as exemplified by a floppy disk drive which has photoelectric sensors such as a TRACK ZERO sensor for sensing whether a transducer head or heads are in the "track zero" position on the floppy disk, and a FILE PROTECT sensor for sensing whether the disk is protected against erasure of any prerecorded data. In order to avoid waste of power, at least the TRACK ZERO sensor, preferably the FILE PROTECT sensor as well, has its light source such as an LED connected to a power supply via a power saving switch herein shown as a switching transistor. Connected to the base of the power saving transistor is a switch control circuit which causes conduction through the transistor, and hence the energization of the sensor light source, only when the operation of the sensor is required, as for a preassigned length of time immediately after the apparatus is electrically turned on.