CONTROLLER AND CONTROL METHOD

A controller (20) for an assistance system (10) configured to execute an assistance operation for a rider of a lean vehicle (1) includes an execution section (22) and an acquisition section (21). The execution section (22) operates the assistance system (10) to execute the assistance operation. The acquisition section (21) acquires a road surface information as information about a road surface (2) on which the lean vehicle (1) is traveling. The execution section (22) operates the assistance system (10) to execute, as the assistance operation, a stop-assistance operation based on the road surface information to assist the rider in stabilizing a stop posture of the rider.