To display an object image without a sense of incongruity in observation even when pixel aspect ratios of objects differ in the case that bit streams of a plurality of objects are decoded by a method such as the MPEG 4, the decoded object images are synthesized and displayed.

An image decoder 4 decodes a coded bit stream S1 of a coded object image. An image conversion ratio calculation device 5 calculates a conversion ratio of an image on the basis of an aspect ratio of an object image and an aspect ratio of a display device. A display position converter 6 converts a display position of the object image into a display position in response to the conversion ratio. An image size converter 7 converts an image size of an object image into an image size in response to the conversion ratio. The object images whose display position and image size are converted are synthesized and displayed.