Abstract: An assist device includes: a first wearing tool mounted to at least a waist portion of a user, an assist arm disposed along a thigh portion of the user and being turnable with respect to the first wearing tool; a motor that generates torque for turning the assist arm; a second wearing tool provided on the assist arm and mounted to the thigh portion; an acceleration sensor provided on the first wearing tool; a rotation detector that detects a turning state of the assist arm; and a control device that controls the motor. The control device includes a processing portion that executes an estimation process of obtaining an estimated weight of a load to be lifted by the user based on an output of the acceleration sensor and an output of the rotation detector, and a control process of controlling the motor based on the estimated weight.