PURPOSE: To obtain an apparatus which enables the minimizing of deterioration in a displacement sensor with easier miniaturization by method wherein light energy is supplied to a shape memory alloy film to cause a thermal displacement and the film is irradiated with illumination light to measure a displacement obtained.

CONSTITUTION: A multi-joint manipulator is constituted of a shape memory alloy film 101 as actuator, a shape memory alloy film heating means 102 and a displacement detection means 103 of the actuator for each joint. The surface of the alloy film 101 is coated with a quantity of reflected light changing means 106 adapted to change in concentration gradually from the end thereof and the rear thereof with a blackbody paint 107. A drive data corresponding to a displacement value of the alloy film 101 is supplied to a voltage setting circuit 112 from outside. The circuit 112 applies a voltage given in the drive data to a semiconductor laser 111 of each joint. The changing means 106 applied on the alloy film 101 is irradiated with a laser light of the laser and the reflected light is converted to a current corresponding to the intensity of the reflected light with a photodiode 113 to be detected with a detection circuit 114.