PURPOSE:To shorten a time when a body to be measured rises up to prescribed temperature by arranging a temperature sensor in the center of a flow cell body, and thus reducing the influence of ambient temperature. CONSTITUTION:A body to be measured which has finished prescribed reaction is flowed into a flow cell body 1 through an inflow duct 7. The temperature of the body to be measured is detected immediately by a temperature sensor arranged in a groove 12 made in the center of the center part 1a of the flow cell body 1 and its detection signal is applied to a prescribed control circuit, whose control signal puts a thermoelectron element 10 as a heat pump. When the temperature of the flow cell body 1 rises up to a prescribed value, the thermoelectron element 10 stops operation and the body in the flow cell body 1 is held at 37 deg.C. After the flow cell body 1 is stabilized at 37 deg.C, the photometry of the body ends, and then the body is discharged from a discharging duct 6, thus completing the photometric operation.