Abstract: In an image encoding apparatus, image information is quantized and variable-length encoding is performed thereon so that the data are stored in a buffer. Thereafter, the data in the buffer are transmitted to the outside at a fixed data rate. At this time, a controller monitors a number of occupied bits in the buffer, and when the number of occupied bits is not more than predetermined thresholds, the controller switches the output of the apparatus to a dummy data generator. At this time, a parameter which is used for rate control is initialized, and dummy data which can be eliminated at a decoding circuit are outputted from the dummy data generator. Furthermore, bit allocation is changed so that a sum of the number of occupied bits and the bit allocation to a frame, which is determined before encoding, does not exceed a fixed amount. Moreover, when the number of occupied bits exceeds the fixed value, a quantization step size is changed to a greater value.