To implement a distributional physical quantity measuring method which reduce false responses.

In this method, distributional physical quantity is measured by transmitting a pseudo-random modulating signal to an object 9 to be measured and demodulating a response signal form the object 9 to be measured. In this case, a reflection attenuating means 10 to attenuate the reflection of the modulating signal is provided at the end part of the object 9 to be measured on the side opposite to the input side of the modulating signal. In addition, light is reflected by the modulating signal, and modulated light is made incident onto an optical fiber to be measured. Then the return light signal due to scattering from the optical fiber to be measured may be demodulated.