A living body optical measurement apparatus of the present invention includes: a light irradiation/measurement unit for irradiating light to an object and measuring the light passed through the object, a signal processing unit for processing measurement data of the light irradiation/measurement unit and creating a living body optical measurement image, and a position measurement unit for measuring positions where light is irradiated to an object and where the passing light is extracted from the object, the light irradiation/measurement unit includes plural optical fibers. The light irradiation/measurement unit includes plural optical fibers, plural optical fiber plugs attached to the plural optical fibers respectively, and a holder fixed detachably at a measurement site of an object and holds the plural optical fiber plugs. The position measurement unit includes a mobile position sensor and an engaging member having a shape detachably engaged with the plural optical fiber plugs attached to the mobile position sensor and held in the holder.