PURPOSE: To improve a detectable fluctuation speed and at the same time simplify a device configuration by outputting a detection signal when detecting the state information of a traveling object to be monitored and stopping the count operation of a clock signal for detecting the timing.

CONSTITUTION: A clock signal inputted externally is counted by a clock counter 2 to judge to see if reflection light is inputted to each state detection element. A state detection element PE for detecting the reflection light outputs a count operation stop signal S2 to the counter 2 to stop counting operation. Then, after the counting operation stops and then a specific amount of time passes, the counting operation of the counter 2 of all state detection elements PE is stopped. Then, a count value comparison means 4 compares count value information S3 of the counter 2 with a comparison value S4 from a comparison value retention means 5 which is set to an optimum time according to the time it takes for each state detection element PE to detect the reflection time.