PURPOSE: To directly measure the load quantity to be applied upon a bearing by mounting a strain measuring element on the supporting side that receives the load of a rotor shaft, and detecting abnormal load by the detection signal thereof.

CONSTITUTION: In the state before placing of a rotor shaft 4 on a bearing 12, the output signal of a load quantity signal converter 24 is so adjusted that the indication of an indicating instrument 25 registers zero. The bearing load by the weight of the rotor shaft 4 while not in operation is beforehand calculated by taking the rotor shaft weight and its centroid position into consideration. Next, the shaft 4 is placed on the bearing 12, and the converter 24 is so adjusted that the instrument 25 registers the bearing load while not in operation. This converter 24 is so arranged as to transmit only the component of the static load by the own weight of the shaft 4 after removing the vibration load component by shaft vibration to the instrument 25. An alarm device which receives the signal of the converter 24 emits an alarm when the bearing signal attains the preset limit value, thereby announcing the abnormality of the bearing load.