PURPOSE: To automatically close the suction valve of a vacuum pad at a window position by automatically detecting the window position of a vehicle constitution body, in the strain removing work which is carried out by adsorbing a shaping plate by a number of vacuum pads and pressing the shaping plate on the vehicle constitution body.

CONSTITUTION: A window position detecting device is constituted of a propagation wave generator such as a speaker and a light which are installed inside a vehicle constitution body and the sensors such as a sound sensor and a light sensor built in a number of vacuum pads 2 on a shaping plate 13 pressed on the vehicle constitution body from outside the vehicle constitution body 5, and when the sensor detects the opened port part, the suction valve of the vacuum pad 2 equipped with the sensor is in closed state. While, the suction valve which is not connected with the vacuum pad 2 which does not detect the opened port part is in opened state. Then, the shaping plate is installed on the vehicle constitution body 5 through adsorption.