Readhead control mechanism and optical encoder

A deadhead control mechanism (400) serves to control a readhead (320) included in an optical encoder (300) that is adapted to measure a mechanical displacement between a fixed portion (100) and a movable portion (200) by reading out a gradation mark on a scale (310) provided on the fixed portion (100), by using the deadhead (320) that is provided on the movable portion (200). The readhead mechanism (400) includes a securing member (410) that secures the deadhead (320) onto the movable portion (200), an actuator (420) that is directly or indirectly secured onto the deadhead 320 to shift the deadhead (320) in an approaching direction or in a distancing direction, and an actuator controller (440) that is adapted to control the actuator (420) to maintain a constant distance between the readhead (320) and the scale (310).