A motion assist device comprising: a joint disposed corresponding to a wearer's bent movable region; a link connected to the joint, the link being installed in the wearer; an actuator configured to drive a motion of the joint; a phase acquisition unit configured to acquire a phase θ' h of a motion of the wearer's bent movable region, wherein the phase acquisition unit includes: an interaction force detection sensor configured to detect interaction force of the motion of the wearer's bent movable region and the motion of the joint; a joint angle sensor configured to detect a joint angle of the joint; and a phase estimation unit configured to estimate the phase θ' h of the motion of the wearer's bent movable region based on the interaction force detected by the interaction force detection sensor and the joint angle detected by the joint angle sensor; the motion assist device further comprising: a target value calculation unit configured to calculate a target value of motion of the joint for synchronizing the motion of the wearer's bent movable region and the motion of the joint while maintaining a preset target phase difference based on a phase oscillator model whose the phase θ' h of the motion of the bent movable region acquired by the phase acquisition unit is an input oscillation, wherein the target value of motion includes a target torque and a target angle, and a drive control unit configured to drive the actuator based on the target value of motion calculated by the target value calculation unit. a joint disposed corresponding to a wearer's bent movable region; a link connected to the joint, the link being installed in the wearer; an actuator configured to drive a motion of the joint; a phase acquisition unit configured to acquire a phase θ' h of a motion of the wearer's bent movable region, wherein the phase acquisition unit includes: an interaction force detection sensor configured to detect interaction force of the motion of the wearer's bent movable region and the motion of the joint; a joint angle sensor configured to detect a joint angle of the joint; and a phase estimation unit configured to estimate the phase θ' h of the motion of the wearer's bent movable region based on the interaction force detected by the interaction force detection sensor and the joint angle detected by the joint angle sensor; the motion assist device further comprising: a target value calculation unit configured to calculate a target value of motion of the joint for synchronizing the motion of the wearer's bent movable region and the motion of the joint while maintaining a preset target phase difference based on a phase oscillator model whose the phase θ' h of the motion of the bent movable region acquired by the phase acquisition unit is an input oscillation, wherein the target value of motion includes a target torque and a target angle, and a drive control unit configured to drive the actuator based on the target value of motion calculated by the target value calculation unit. an interaction force detection sensor configured to detect interaction force of the motion of the wearer's bent movable region and the motion of the joint; a joint angle sensor configured to detect a joint angle of the joint; and a phase estimation unit configured to estimate the phase θ' h of the motion of the wearer's bent movable region based on the interaction force detected by the interaction force detection sensor and the joint angle detected by the joint angle sensor; the motion assist device further comprising: a target value calculation unit configured to calculate a target value of motion of the joint for synchronizing the motion of the wearer's bent movable region and the motion of the joint while maintaining a preset target phase difference based on a phase oscillator model whose the phase θ' h of the motion of the bent movable region acquired by the phase acquisition unit is an input oscillation, wherein the target value of motion includes a target torque and a target angle, and a drive control unit configured to drive the actuator based on the target value of motion calculated by the target value calculation unit. a target value calculation unit configured to calculate a target value of motion of the joint for synchronizing the motion of the wearer's bent movable region and the motion of the joint while maintaining a preset target phase difference based on a phase oscillator model whose the phase θ' h of the motion of the bent movable region acquired by the phase acquisition unit is an input oscillation, wherein the target value of motion includes a target torque and a target angle, and a drive control unit configured to drive the actuator based on the target value of motion calculated by the target value calculation unit.