To enhance the reliability and accuracy of measurement data by sorting the period data of detection pulse in the order of magnitude, discarding large and small data thereof, and averaging the remaining data to prepare physical quantity data thereby discriminating a signal from a noise.

A period measuring circuit 2 measures each period between respective rising or falling and next rising of falling or a vehicle speed pulse, i.e., a detection pulse, from a sound velocity sensor 1 and stores the measurement sequentially in a memory circuit 3. A specified number of stored vehicle speed pulses are then rearranged in the order of numerical value by a sorting means 4 before being stored in a register 5. Large and small data are then discarded therefrom as noises and only the central values are fed to an averaging circuit 6. The averaging circuit 6 averages the vehicle data simply to produce a vehicle data having improved S/N ration which is delivered to a microcomputer in order to prepare display data, control data, and the like.