To provide an encoding method conversion device capable of further reducing delay time when starting reproduction of moving image data after conversion, and efficiently performing processing related to the reduction.

The image encoder includes: a moving image decoding part 101 for decoding first moving image data; a delay time extraction part 103 for extracting information indicating buffer initial delay time, included in the first moving image data; a determination part 105 for determining whether the first moving image data is encoded for each frame; a delay time determination part 104 for determining a smaller value than the extracted buffer initial delay time as the buffer initial delay time after conversion when the first moving image data is determined to be encoded for each frame; and a moving image encoding part 102 for encoding the decoded first moving image data for each field in the second encoding method to set the determined buffer initial delay time after conversion.