Measurement apparatus

A measurement apparatus, comprising:

• a flow path device 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 an 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,
• a calibration region for calibrating the optical sensor, and
• a non-reflection member disposed on a side of the flow path device 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 including a light emitting element and a light receiving element 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 on a circumference along which the optical sensor moves in accordance with a rotary drive of the arm-like member.