An optical measurement apparatus can be provided, in which the sample is optically measured without loss of the illuminating light with high sensitivity. A glass plate as the transparent member 50 is placed in the interface between the end face 43 of the optical waveguide 40 guiding the illuminating light L generated by the laser light source 20 and the wall face of the capillary 30. According to the above feature, the air layer is prevented from existing in the interface between the end face 43 of the optical fiber 40 and the wall face of the capillary 30, thus the sample S can be optically measured with high sensitivity and few variability without causing the loss of the illuminating light L.