Disclosed herein is an arithmetic decoding apparatus including an instruction decoder configured to decode an arithmetically encoded data decoding instruction to be executed for carrying out an arithmetic-decoding process of arithmetically decoding arithmetically encoded data into a binary signal; an execution condition code holding section configured to hold the binary signal obtained as a result of an immediately preceding arithmetic-decoding process as an execution condition code; and an arithmetic decoding execution section configured to determine whether a context number specified by the arithmetically encoded data decoding instruction is to be used as a context index as it is or the specified context number incremented by 1 is to be used as the context index in accordance with the execution condition code, and carry out the arithmetic decoding process by making use of the determined context index.