PURPOSE: To detect only the light emitting pulse with high efficiency to improve the detecting accuracy, by providing a filter at a photodetecting circuit which detects a nonsounding groove and accordingly lowering the sensitivity due to the outer disturbing light.

CONSTITUTION: The revolution of an arm driving motor 1 is transmitted to a driving system, and a slide base 4 can be moved toward a guide rail. At the same time, a pulse generating disk 4 connected directly to a worm gear. Thus an arm position detecting LED 13 and a phototransistor 14 set opposite to the disk 14 can detect the pulse proportional to a shift distance of the arm through a slit drilled to a pulse generating disk 2. A cartridge 6 also shifts on the surface of a record as the base 4 moves. In this case, a pair of LED 10 and phototransistor 11 incorporated to the cartridge 6 detect both nonsounding groove and sounding groove. These sounding grooves can be processed by a microcomputer 9 along with the pulse count for detection of the arm position.