An attenuated-total-reflection measurement apparatus 10 of the present invention collects light onto a contact surface between a sample and an ATR prim 14 at an incident angle greater than or equal to a critical angle and measures total-reflection light from the contact surface. The attenuated-total-reflection measurement apparatus 10 comprises: a light-irradiating system 12 for emitting the light which is collected onto the contact surface; a photodetector 18 for detecting the total-reflection light from the contact surface; an aperture 20 for restricting the light which the photodetector 18 detects to only light from a specific measurement site in the contact surface; and a detection-side scanning mirror 22 provided in a light path extending from the ATR prism 14 to the aperture 20. The detection-side scanning mirror 22 is configured to allow the orientation of a reflecting surface thereof to be changed. And the measurement site in the contact surface, which is to be measured with the photodetector 18, is changed by moving the reflecting surface of the detection-side scanning mirror 22 with respect to the total-reflection light from the contact surface, to perform mapping measurement in the contact surface.