An object of the invention is to provide a structure for coupling two rotary shafts, which can be made smaller in size. A driving shaft for pumps is rotatably supported by a first bearing and a second bearing, while a rotary shaft of an electric motor is rotatably supported by the second bearing and a third bearing. Each one end of the driving shaft and the rotary shaft is inserted into the common second bearing, so that rotation of the rotary shaft is transmitted to the driving shaft.