To finely correct magnetic recording information writing frequency with reference to a film feeding speed.

The film feeder is provided with a feeding means 4 for feeding a film 8 with perforations, a detecting means 10 for detecting the hole width of the perforation along a feeding direction, a calculating means for comparison- calculating plural bits of hole width detecting information detected by the detecting means 10 and calculating the film 8 feeding speed, and a magnetic recording information writing means 13 for varying the magnetic recording information writing frequency in accordance with the feeding speed calculated by the calculating means.