To prevent measurement errors and prevent generating failures in an optical communication device, by regularly monitoring the level of a disturbance light in a communication light, or the like, for transmitting an optical fiber line to be tested during optical pulse test.

An optical pulse Po is emitted to an optical fiber line 1 from a pulse light source 21, and a light that returns to a first coupler 22 in a first period is made incident to a second coupler 23. A first optical component Pb emitted from the second coupler 23 at high transmittance is made incident to a characteristics calculation means 31, and processing required for detecting the characteristic of the optical fiber line 1. In a second period, wherein the following optical pulse is made incident after the first period passes, a second optical component Pc emitted from the second coupler 23 at low transmittance is made incident to an intensity detection means 32 to detect its intensity Wx, and the detected intensity Wx is compared with a reference Wr by a comparison means 33. A control means 35 controls interrupt and restart of the emission of optical pulse and the processing of characteristic calculation required for optical pulse test, on the basis of the comparison result.