To calculate an image quality degradation degree close to subjective evaluation from received video encoded data only.

When deciding that data of which decoding processing is performed include a discontinuous point, a degraded area detection part 172 specifies input data from the discontinuous point to the next decoding processing synchronous position, generates information relating to an image area wherein image quality is degraded by the influence of the discontinuous point as the result of the decoding processing as degraded area information, and outputs it to a degraded area importance degree calculation part 173. The degraded area importance degree calculation part 173 calculates an importance degree according to subjectivity on the image frame of a degraded area from the degraded area information received from the degraded area detection part 172, and notifies an image quality degradation degree calculation part 174 of the degraded area information and the importance degree. The image quality degradation degree calculation part 174 calculates an image quality degradation degree on the basis of the degraded area information and the importance degree of the degraded area calculated in the degraded area importance degree calculation part 173 for each degraded area detected in the degraded area detection part 172, and outputs the image quality degradation degree to the outside.