To solve the problem that an object part projected on only one of two key frames at the time of generating an intermediate image based on a key frame.

A stream separating part 44 extracts a key frame KF, a separated external frame area FA and corresponding point information CP from an encoded data stream DS. The extracted key frame KF and the corresponding point information CP are transmitted to an intermediate image generating part 22, and an intermediate image is generated based on them. On the other hand, the external area FA is transmitted to an external frame changing part 48, and replaced with the external frame area of the generated intermediate image.