A biological signal measuring apparatus includes: a light emitter which emits at least two light beams having different wavelengths to living tissue of a subject； a light receiver which receives the light beams that are emitted from the light emitter and transmitted through or reflected from the living tissue, and which converts at least one of the light beams to at least one electric signal that corresponds to a reception light intensity of the at least one of the light beams； a detector which detects temporal variation of the reception light intensity from the electric signal； a selector which selects a pulse oximeter mode in which at least one of an oxygen saturation and a pulse rate is calculated and a capillary refilling time measurement mode in which a capillary refilling time is calculated； and a calculator which, based on the temporal variation of the reception light intensity, performs a calculation in the mode that is selected by the selector.
