The present invention aims to reduce the code length and time for flushing the code. An encoding apparatus includes a data memory storing information source data, a learning memory storing learning data relating the encoding data, a probability estimation table for outputting an encoding parameter indicated by the learning data, and an encoder outputting the code by implementing an arithmetic encoding based on the encoding data and the encoding parameter. In the above encoding apparatus, according to the present invention, a synchronization detector is provided measuring one of inputting the information source data and outputting the code at a predetermined interval. Further, the encoding apparatus includes a boundary detector detecting a carry boundary value within the effective region at predetermined interval and instructing to truncate a part of the effective region based on the detection result. The encoder truncates one of equally divided upper and lower partial regions of the effective region indicated by the carry detector and updates the effective region.