PURPOSE:To make it possible to always and accurately measure a car height without being affected by the state of a road surface, by correcting a measured value on the basis of the rising characteristics of a receiving wave returned while reflected from the road surface. CONSTITUTION:The ultrasonic pulse transmitted from a transmitter 3 is reflected at a road surface 4 and the reflected pulse is received by a receiver 5. This receiving output is respectively applied to a wave form shaping circuit 8 and a wave form rising circuit 16 through an amplifier 6 and a rectifier circuit 7. In this case, when the receiving wave becomes weak by the state of the road surface, the rising of the output wave form of the rectifier circuit 7 becomes gentle to generate a measuring error. Hereupon, an analytical circuit 16 receives the output of the rectifier circuit 7 to measure the rising characteristics of the receiving wave ans a correction value N is fabricated based on this rising characteristics. Subsequently, this correction value and the output of the wave form shaping circuit 8 are inputted to a micro CPU15 for operating car height. By this method, the car height can always accurately measured without being affected by the state of the road surface.