To adjust air pressure of an air cylinder simply and correctly, in a device balancing a controlled object displaceable in the fixed direction due to gravity on a fixed position by the air pressure of the air cylinder.

This robot device is constituted so that the position of a vertically moving shaft supported to be displaceable in the direction of gravity by an arm is controlled by means of a motor, and the device is provided with an air cylinder balancing the vertically moving shaft on a fixed position, for preventing the motor from being subjected to a large load due to gravity applied to the shaft. In this case, at adjusting the air pressure of the air cylinder, current of the motor is controlled so as to hold the shaft, and from the current indicated value or the actual current, overs and shorts portion of the air pressure is computed as the required air pressure Pa (110, 120). Based on the computed result, the adjusting method (increase/decrease direction, completion of adjustment) is indicated (130-150) to an adjustment operator. As a result, the air pressure can be adjusted simply and correctly.