A liquid component concentration meter measures the concentration of a liquid in a liquid supply tube from outside the liquid supply tube. The concentration meter includes a liquid supply tube; a light transmission unit; a light emission unit for irradiating light to the light transmission unit; a light reception unit for receiving light passed through the light transmission unit; a support member that movably supports the light emission unit and the light reception unit such that a measurement position is moved along the light transmission unit; a measurement-position moving mechanism for moving the support member such that the measurement position is moved within a predetermined area in the light transmission unit; and a data processing unit for calculating the concentration of the liquid in the liquid supply tube based on intensities of light received by the light reception unit at different measurement positions.