The bioinstrumentation apparatus 10 includes a light irradiation unit irradiating a measurement region B with light, a light detection unit detecting diffused light from the measurement region, and a computing unit 14 generating a reconstructed image for the interior of the measurement region. The computing unit 14 calculates J coefficients w j set for every pixel of the reconstructed image and more than 0 and not more than 1 (where J is the number of pixels of the reconstructed image) and carries out successive approximation computation by the following iterative formula x j k + 1 = x j k + w j �¢ d j k (where k is an integer from 1 to N, N is the number of times of iterative computation, x j (k) is a pixel value of the jth pixel on the kth iterative computation, and d j (k) is an update amount of the jth pixel on the kth iterative computation) to generate the reconstructed image. Thereby, there are provided a bioinstrumentation apparatus and an image generating method capable of suppressing a difference in spatial resolution and noise characteristics depending on a position inside the measurement region to generate an image which is uniform to a greater extent.
