A measurement apparatus (1, 1A), comprising: an optical sensor, a flow path device (2, 2A) having an upper and a lower surface, including a first flow path in which first liquid including particles to be measured is flowed, and which includes a measurement region where the particles in the first liquid are measured with said optical sensor, a second flow path in which second liquid for comparison which does not include the particles is flowed, and which includes a comparison region where the second liquid is measured with the optical sensor, wherein said optical sensor is disposed on the side of the upper surface of the flow path device (2,2A) or on the side of the lower surface of the flow path device (2,2A), a calibration region for calibrating the optical sensor, and a non-reflection member disposed on a region overlapped with the first flow path and the second flow path on a side of the flow path device (2, 2A) that is opposite to the optical sensor, and that corresponds to the measurement region and the comparison region; an arm-like member in which the optical sensor in which a light emitting element and a light receiving element are integrally disposed on one substrate is disposed in a first end, and in which a drive shaft is disposed in a second end; and a rotary drive actuator connected to the drive shaft and configured to rotationally drive the arm-like member in a predetermined range, wherein each of the measurement region, the comparison region, and the calibration region is disposed as a region including a circumferential position along which the optical sensor moves in accordance with a rotary drive of the arm-like member, and wherein the non-reflection member blocks a reflection of light emitted from the light emitting element that has passed through each of the first flow path in the measurement region and the second flow path in the comparison region, and blocks disturbance light entering the first flow path and the second flow path from the side opposite to the optical sensor. an optical sensor, a flow path device (2, 2A) having an upper and a lower surface, including a first flow path in which first liquid including particles to be measured is flowed, and which includes a measurement region where the particles in the first liquid are measured with said optical sensor, a second flow path in which second liquid for comparison which does not include the particles is flowed, and which includes a comparison region where the second liquid is measured with the optical sensor, wherein said optical sensor is disposed on the side of the upper surface of the flow path device (2,2A) or on the side of the lower surface of the flow path device (2,2A), a calibration region for calibrating the optical sensor, and a non-reflection member disposed on a region overlapped with the first flow path and the second flow path on a side of the flow path device (2, 2A) that is opposite to the optical sensor, and that corresponds to the measurement region and the comparison region; an arm-like member in which the optical sensor in which a light emitting element and a light receiving element are integrally disposed on one substrate is disposed in a first end, and in which a drive shaft is disposed in a second end; and a rotary drive actuator connected to the drive shaft and configured to rotationally drive the arm-like member in a predetermined range, wherein each of the measurement region, the comparison region, and the calibration region is disposed as a region including a circumferential position along which the optical sensor moves in accordance with a rotary drive of the arm-like member, and wherein the non-reflection member blocks a reflection of light emitted from the light emitting element that has passed through each of the first flow path in the measurement region and the second flow path in the comparison region, and blocks disturbance light entering the first flow path and the second flow path from the side opposite to the optical sensor.