To provide a length energization variable alloy thin-wire actuator capable of obtaining a large stroke distance with a short shape memory alloy wire, providing reductions in the number of parts and size, eliminating problems of friction, and obtaining an arc motion as well as a reciprocating motion.

One end of an elastic member 2 in a prescribed length is fixed at a base 3, and the length excitation variable alloy (shape memory alloy) flexible thin-wire 1 of which the length is contracted when current is flowed and returns to an original length when the current is cut off is crossed over at a middle position in a length direction of the elastic member 2 in a V shape. Both of the ends are fixed at the alloy wire fixing positions 5, 5 of the base 3 to flow the current from these. The elastic member 2 is pressed down because the length of the shape memory alloy wire 1 is contracted when the current is flowed, and the elastic member 2 is raised to the original position because the length returns to the original when the current is cut off. When the length of the elastic member 2 is increased, the motion of a top end 7 becomes large.