The optical signal sampling apparatus and the optical signal monitor apparatus are configured of an optical combiner for combining an optical signal to be sampled and a sampling light pulse with each other and an electroabsorption modulator. The electroabsorption modulator has two optical terminals for inputting/outputting the light and a power supply terminal for applying the electric field to the optical path connecting the two optical terminals, and has such a characteristic that the absorption rate of the light propagating through the optical path changes in accordance with the magnitude of the electric field, the light emitted from the optical combiner is received by one of the two optical terminals, and the absorption rate is increased when the sampling light pulse is not incident while the absorption rate is decreased when the sampling light pulse is incident. Further, the apparatuses include a DC power supply for applying a predetermined DC voltage to the power supply terminal and an optical separator for selectively emitting the optical signal component to be sampled, of the optical signals emitted from another of the two optical terminals.