This invention reliably encodes an image while continuously inputting the image with a relatively simple configuration. For this purpose, in this invention, input image data is encoded by an encoder (102) and stored in first and second memories. An encoding sequence controller (108) monitors the code amount. Upon determining that the code amount has reached a set value, the encoding sequence controller discards the data in the first memory and instructs the encoder (102) to increase the quantization step and continue encoding. Preceding encoded data is stored in the second memory. The encoded data is re-encoded by a re-encoder (109) using the same quantization step as that of the encoder (102) after the parameter is changed. The re-encoded data is stored in the first and second memories. The quantization steps set in the encoder (102) and re-encoder (109) at this time have such values that re-encoding by the re-encoder (109) is ended before time when the code amount reaches the set value again.