The distance between an image indicating a measured portion and a measuring apparatus is previously registered, a measured object is arranged in a prescribed space in a non-contact state, the position of a probe is so adjusted that two-dimensional image sensing means senses the previously registered image of the measured portion, the position of the probe is so adjusted that the distance up to the measured portion by distance measuring means reaches the previously registered distance, and orientation determination means irradiates the measured portion with a light beam while changing the orientation for determining an orientation maximizing the quantity of light transmitted through the measured portion. Thereafter the physical quantity measuring apparatus irradiates the measured portion with measuring light and senses output light from the measured portion for obtaining a physical quantity.