Abstract: A respiration information obtaining apparatus includes: a light emitter configured to emit a first light including a first wavelength and a second light including a second wavelength different from the first wavelength; a light detector that outputs a first signal and a second signal respectively corresponding to an intensity of the first light and an intensity of the second light after an interaction with a tissue of a subject, and a processor that calculates an index value based on a ratio between the first signal and the second signal, and obtains respiration information of the subject based on a change over time in the index value.