At the time of start of usage, a voltage to be applied to a shape memory alloy wire 102 by a feedback control circuit 120 is set to a first voltage value (step S1), and at a limit resistance value detection step, (the feedback control circuit) measures a limit resistance value when the shape memory alloy wire 102 can be contracted (step S2), and upon storing the limit resistance value, a value of the maximum voltage to be input by the feedback control circuit 120 is set to a second voltage value (step S3). At an input electric power optimization step, a target resistance value is indicated, and the feedback control is carried out such that the resistance value indicated is not lower than the limit resistance value (step S4). Thereafter, voltage is stopped at the time of stopping the use of the actuator.