A blood flow measuring apparatus (20, 800, 900) comprising: a sensor unit (24, 700, 820, 930) including a light emitting part (120, 950) configured to emit light onto a measurement area; at least two light receiving parts (130, 960, 962) configured to receive the light transmitted through the measurement area; and a control part (30, 830, 940) configured to measure a blood flow state of the measurement area according to signals outputted by the light receiving parts (130, 960, 962), wherein the light emitted by the light emitting part (120, 950) is received by the light receiving parts (130, 960, 962) arranged at different distances from the light emitting part (120, 950) and the light receiving parts (130, 960, 962) are adapted to output the signals responsive to the received light; the control part (30, 830, 940) is adapted to measure the blood flow state of the measurement area by performing an arithmetic process to cancel a component of oxygen saturation in the blood, said component being included in the signals outputted by the light receiving parts (130, 960, 962), characterized in that the sensor unit (24, 700, 820, 930) includes an optical path separating member (140, 720, 970) configured to have different refraction indexes with respect to light that proceeds from the light emitting part (120, 950) to the measurement area and light that proceeds from the measurement area to the light receiving part (130, 960, 962) that is included in the sensor unit (24, 700, 820, 930); and the light emitting part (120, 950) is adapted to emit the light and said light receiving part (130, 960, 962) included in the sensor unit (24, 700, 820, 930) is adapted to receive the light through the optical path separating member (140, 720, 970), and in that the light emitting part (120, 950) is adapted to emit first light having a wavelength that is hardly influenced in an optical characteristic by the oxygen saturation in the blood and second light having a wavelength that is influenced in an optical characteristic by the oxygen saturation in the blood, and the control part (30, 830, 940) is adapted to calculate the red blood cell concentrations as a function of only hematocrit (Ht), that is a volume concentration of red blood cells per unit volume, by calculating the ratio of red blood cell concentration measured with the first light to that measured with the second light emitted by the light emitting part. a sensor unit (24, 700, 820, 930) including a light emitting part (120, 950) configured to emit light onto a measurement area; at least two light receiving parts (130, 960, 962) configured to receive the light transmitted through the measurement area; and a control part (30, 830, 940) configured to measure a blood flow state of the measurement area according to signals outputted by the light receiving parts (130, 960, 962), wherein the light emitted by the light emitting part (120, 950) is received by the light receiving parts (130, 960, 962) arranged at different distances from the light emitting part (120, 950) and the light receiving parts (130, 960, 962) are adapted to output the signals responsive to the received light; the control part (30, 830, 940) is adapted to measure the blood flow state of the measurement area by performing an arithmetic process to cancel a component of oxygen saturation in the blood, said component being included in the signals outputted by the light receiving parts (130, 960, 962), characterized in that the sensor unit (24, 700, 820, 930) includes an optical path separating member (140, 720, 970) configured to have different refraction indexes with respect to light that proceeds from the light emitting part (120, 950) to the measurement area and light that proceeds from the measurement area to the light receiving part (130, 960, 962) that is included in the sensor unit (24, 700, 820, 930); and the light emitting part (120, 950) is adapted to emit the light and said light receiving part (130, 960, 962) included in the sensor unit (24, 700, 820, 930) is adapted to receive the light through the optical path separating member (140, 720, 970), and in that the light emitting part (120, 950) is adapted to emit first light having a wavelength that is hardly influenced in an optical characteristic by the oxygen saturation in the blood and second light having a wavelength that is influenced in an optical characteristic by the oxygen saturation in the blood, and the control part (30, 830, 940) is adapted to calculate the red blood cell concentrations as a function of only hematocrit (Ht), that is a volume concentration of red blood cells per unit volume, by calculating the ratio of red blood cell concentration measured with the first light to that measured with the second light emitted by the light emitting part.