PURPOSE: To reduce the load on a microcomputer by inputting the pulse signal of a sensor part not directly, but preprocessing the pulse signal by a counting means united with the sensor part and a storage part such as a shift register as a storage part.

CONSTITUTION: The sensor part 1 detects rotation and continues to send the pulse signal to a counter part 2. The counter part 2 counts up every time the pulse signal is inputted. When a trigger pulse signal is inputted from a controller to a terminal 7, a timing generation part 4 outputs a timing signal for stopping the counting operation of the counter 2 temporarily and transferring the data of the counter part 2 to the storage part 3. When the data is latched in the storage part 3, the generation part 4 outputs a timing signal for switching the storage part 3 to a serial side and clearing and restarting the counter part 2. The storage part 3 outputs the contents of the data from a terminal 5 with a clock signal inputted from a clock signal input terminal 6. A controller receives this output signal and calculates the rotating speed.