Abstract: The present invention relates to a thin film heater (2) including a thin film heat-producing resistor, and a first and a second thin film electrodes (22, 24) electrically connected to the thin film heat-producing resistor to apply voltage to the thin film heat-producing resistor. In the thin film heater (2), at least part of the thin film heat-producing resistor is light transmissive. Preferably, the first thin film electrode (22), the thin film heat-producing resistor and the second thin film electrode (24) are laminated in the film thickness direction in the mentioned order. The present invention further provides an analytical instrument (X) provided with the thin film heater (2).