A motion assisting device comprises a first index value measuring means 65 which measures a first index value indicating a remaining energy amount of an electrical storage device 19 and power regulation means 63 and 64 each of which regulates the motive power of an electric actuator 9 after the time point of measuring the first index value at least according to the first index value measured by the first index value measuring means 65. The power regulation means 63 and 64 regulate the motive power of the electric actuator 9 so that the remaining energy amount of the electrical storage device 19 is maintained at a predetermined lower limit or greater until the end time point of a desired operating time of the motion assisting device A.