PURPOSE: To prevent outputting of a distance of an object unnecessary to be detected from being generated by providing deciding means for measuring a varied amount of a distance each time the distance is measured to decide invalid when the varied amount exceeds a predetermined value.

CONSTITUTION: When a light pulse-emitted from transmitting means 1 is emitted to an object 6, it is reflected, and the reflected light is received by receiving means 2. Then, processing means 3 obtains a distance from a distance measuring apparatus and the object 6 from a reciprocating time of the light pulse. In this case, distance deciding means 36 compares a distance of this time with the previous distance each time the distance is measured and obtains its varied amount. As a result, when the amount exceeds a predetermined value, whether the state of the predetermined value or more is continued for a predetermined time or not is decided. When it is continued for the predetermined time, the distance of this case is output. On the other hand, when it is not continued for the predetermined time, the distance of the case is decided invalid, and the previous distance is output to output means 34.