PURPOSE: To provide an average load controller which does not cause the control conditions to vary and can keep the load redius almost constant, by performing control with an average load both in a slow rotation range and in a rapid rotation range.

CONSTITUTION: A working oil is supplied to a cylinder 8 to move a tire mounting part 6 forth to bring a tested tire 4 into contact with a rotary drum 1 under a predetermined load. A running test of the tire 4 is conducted by rotating the rotary drum. A pulse pickup unit 12 is attached to a tire mounting shaft 5. A load detector 13 is provided between the tire mounting shaft 5 and the tire mounting part 6 to detect the real load acting on the tire. The signal of the detector 13 is entered into an average load calculation circuit 15 to determine the average value of the load after each rotation of the tire 1. A servo-amplifier 17 generates a deviation signal on the basis of the output signal of the average load calculation circuit 15 and a setpoint signal of a setting unit 16 to operate a servo-valve 11 to control the cylinder 8.