A method and an apparatus for diagnosis of a motor-operated valve for determining the degree of abnormality of the motor-operated valve in which rotational driving force of a driving motor 1 is mechanically transmitted to drive a valve disc 8 to an open or close position. The on-off timing of driving energy to the driving motor 1 is determined based on signal information from a plurality of magnetisms sensors 16 attached to a power cable tube 15 housing a power cable 14 or control line for driving the driving motor 1. The timing when the driving energy to the driving motor 1 is turned on and off when the valve disc 8 is shifted to an open or close position can be determined precisely.