A common optical pickup can be mounted in any of disc drive units having respective pairs of oppositely disposed guide shafts that are separated from each other by different distances. The present invention provides an adaptor member for allowing an optical pickup currently mounted in a first disc drive unit having respective main shaft and sub shaft arranged oppositely relative to and in parallel with each other and separated from each other by a distance to be mounted in a second disc drive unit having respective main shaft and sub shaft arranged oppositely relative to and in parallel with each other and separated from each other by a distance, the distance separating the main shaft and the sub shaft of the first disc drive unit being smaller than the distance separating the main shaft and the sub shaft of the second disc drive unit, the adaptor member being adapted to be fitted to a second supporting section of the optical pickup mounted in the first disc drive unit, the second supporting section being formed with a guide groove for pinching the sub shaft and arranged opposite to a first supporting section formed with a guide hole for allowing the main shaft to run through it, the adaptor member having a guide groove for pinching the sub shaft of the second disc drive unit.