A virtual reference decoder device 300 comprises: an extraction unit determination unit 301 that defines a unit for extracting from an encoded image buffer 112/209; an extraction timing determination unit 302 that determines a timing for extracting from the encoded image buffer 112/209; an extraction unit 303 that extracts, at the extraction timing, encoded data in a unit for extracting from an encoded image buffer 112/209; and a determination unit 304 that determines whether the encoded data can be decoded, in accordance with the amount of change in the buffer volume of the encoded image buffer 112/209 between two predetermined extraction timings.