1. A situation recognition apparatus that recognizes a current situation by using optical information, the apparatus comprising: an optical information acquisition unit configured to acquire optical information; a storage configured to store a plurality of pieces of optical information; a processing unit configured to match a plurality of the pieces of optical information stored in the storage and optical information newly acquired by the optical information acquisition unit; and an output unit configured to output a result of the matching; wherein the storage further stores a probabilistic model that numerically represents transitions between the plurality of pieces of optical information; wherein the processing unit includes a difference calculation section that obtains differences between the plurality of pieces of optical information and the newly acquired optical information, respectively, and calculates a value indicative of the differences; a difference storage section that stores the calculated value indicative of the differences in time order; and a matching processing section that performs matching by using a time sequence of a plurality of the stored values indicative of the differences and the probabilistic model.