A disturbance load estimation method for a servomotor in which an disturbance load externally exerted on the servomotor can be accurately estimated even when the voltage is saturated. Actual values (Ir, Is, It) of three-phase alternating current determined by current loop processing (term 1) are converted by DQ conversion, and an effective current component (Iq) that contributes to a torque generated by the servomotor is obtained (term 4). Based on the obtained effective current component, a motor acceleration is estimated (term 5), a difference between the estimated acceleration and an actual motor acceleration (term 6) is obtained, and the disturbance load is estimated based on the acceleration difference (term 7).