In measurement data selection, when a vector composed of measurement data obtained for respective combinations of light emitting positions, light detection positions, and resolving times in a time-resolved waveform is given as y, a vector in which pixel values of learning image data are components is given as x, and a system matrix for calculating internal image data from the measurement data is given as A1, the vector y which meets the conditional expressions (2) and (3) min&spar；y&spar；00&emsp；&emsp；(2), &spar；x&minus；A1Ty&spar；22&nlE；&egr；2&emsp；&emsp；(3) or the conditional expression (4) min(&spar；y&spar；00+&bgr；&spar；x&minus；A1Ty&spar；22)&emsp；&emsp；(4) is determined, and upon measurement of a subject, only the measurement data corresponding to nonzero components of the vector y is used to prepare the internal image data.
