The present invention provides an attenuated-total-reflection ("ATR") measurement apparatus that collects light onto a contact surface between a sample and an ATR prism 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 according to the invention includes: a light-irradiating system for emitting the light which is collected onto the contact surface; a photodetector for detecting the total-reflection light from the contact surface; an aperture for restricting the light which the photodetector detects to only light from a specific measurement site in the contact surface; and a detection-side scanning mirror provided in a light path extending from the ATR prism to the aperture.