A compressor assembly comprising: a rotation shaft; a rotor core, mounted on one end side of the rotation shaft; a compressor wheel (100; 200; 300; 400; 500) mounted on another end side of the rotation shaft; bearings (56, 58), supporting the rotation shaft; and a casing enclosing a part of the rotation shaft, the rotor core and the bearings (56, 58), wherein the compressor wheel includes: a boss portion mounted on a rotation shaft; a rear plate portion (102; 302) disposed on an opposite side of a tip end portion disposed on one end side of the boss portion, the rear plate portion extending perpendicular to an axial direction of the rotation shaft; and a sensor detection surface (110; 310) formed on a circumferential surface of the tip end portion of the boss portion or on a vertex side of a circumferential surface of the rear plate portion, the sensor detection surface (110; 310) being inclined to the circumferential surface of the end portion or the circumferential surface of the rear plate portion, the sensor detection surface (110; 310) being detectable by an optical sensor that irradiates the sensor detection surface (110; 310) with light and detects light reflected therefrom; and a balance cut portion (105; 305), disposed on the circumferential surface of the tip end portion of the boss portion or on the circumferential surface of the rear plate portion, the balance cut portion (105; 305) being a part of the circumferential surface (104b, 302a) that is cut, and wherein the sensor detection surface (110; 310) has an inclined angle, adapted to allow an optical sensor to distinguish and detect the sensor detection surface (110; 310) from the balance cut portion (105; 305). a rotation shaft; a rotor core, mounted on one end side of the rotation shaft; a compressor wheel (100; 200; 300; 400; 500) mounted on another end side of the rotation shaft; bearings (56, 58), supporting the rotation shaft; and a casing enclosing a part of the rotation shaft, the rotor core and the bearings (56, 58), wherein the compressor wheel includes: a boss portion mounted on a rotation shaft; a rear plate portion (102; 302) disposed on an opposite side of a tip end portion disposed on one end side of the boss portion, the rear plate portion extending perpendicular to an axial direction of the rotation shaft; and a sensor detection surface (110; 310) formed on a circumferential surface of the tip end portion of the boss portion or on a vertex side of a circumferential surface of the rear plate portion, the sensor detection surface (110; 310) being inclined to the circumferential surface of the end portion or the circumferential surface of the rear plate portion, the sensor detection surface (110; 310) being detectable by an optical sensor that irradiates the sensor detection surface (110; 310) with light and detects light reflected therefrom; and a balance cut portion (105; 305), disposed on the circumferential surface of the tip end portion of the boss portion or on the circumferential surface of the rear plate portion, the balance cut portion (105; 305) being a part of the circumferential surface (104b, 302a) that is cut, and wherein the sensor detection surface (110; 310) has an inclined angle, adapted to allow an optical sensor to distinguish and detect the sensor detection surface (110; 310) from the balance cut portion (105; 305). a boss portion mounted on a rotation shaft; a rear plate portion (102; 302) disposed on an opposite side of a tip end portion disposed on one end side of the boss portion, the rear plate portion extending perpendicular to an axial direction of the rotation shaft; and a sensor detection surface (110; 310) formed on a circumferential surface of the tip end portion of the boss portion or on a vertex side of a circumferential surface of the rear plate portion, the sensor detection surface (110; 310) being inclined to the circumferential surface of the end portion or the circumferential surface of the rear plate portion, the sensor detection surface (110; 310) being detectable by an optical sensor that irradiates the sensor detection surface (110; 310) with light and detects light reflected therefrom; and a balance cut portion (105; 305), disposed on the circumferential surface of the tip end portion of the boss portion or on the circumferential surface of the rear plate portion, the balance cut portion (105; 305) being a part of the circumferential surface (104b, 302a) that is cut, and wherein the sensor detection surface (110; 310) has an inclined angle, adapted to allow an optical sensor to distinguish and detect the sensor detection surface (110; 310) from the balance cut portion (105; 305).