The present invention provides a technology which precisely restores a distribution of original information by carrying out an iterative calculation based on a distribution of degraded information and a transfer function including a phase characteristic of a transfer system. A method according to the present invention restores the original information using the degraded information and the transfer function in the frequency space. The method according to the present invention considers a distribution of the degraded information and a distribution of the original information as distributions of probability density functions, and considers the transfer function as a probability density function of a conditional probability. The most probable distribution of the original information according to the distribution of the degraded information is acquired by the iterative calculation by means of relational equations based on the Bayes' theorem relating to the probability density functions.