Abstract: An optical distance measuring apparatus having measurement error compensating function for compensating the measurement error due to electromagnetic induction noise which would lower the accuracy in distance measurement. According to the optical distance measuring apparatus of the present invention, the distance from the apparatus to the target is given by the difference in optical path between an "external optical path" to a corner-cube prism, i.e. the external target, and an "internal reference optical path". The measurement error can be cancelled by the periodicity of the measurement error curve and the predetermined length of the optical path extension means. Thus the measurement error can be compensated for and therefore a measured distance value free of measurement error can be obtained from the distance measuring apparatus.

Abstract: A delay time measuring device for measuring a delay time of continuous pulses wherein the averaging effect is improved. The device comprises a rough estimation counter means and a precision measuring means, and the rough estimation counter means makes a rough measurement of a delay time by counting clocks of a reference signal generating means between a starting pulse and a stopping pulse. The precision measuring means performs a precision measurement of a delay time by synchronizing an output signal of a voltage controlled oscillator with the stopping pulse and measuring a difference in phase between the output signal of the voltage controlled oscillator and a signal generated by the reference signal generating means. Then, a delay time of pulses is measured by synthesizing a rough measured value by the rough estimation counter with the precision measured value.