Abstract: PID information and TSC information are extracted from a header of received data inputted to a terminal 1 and are supplied to an IDT (16). The IDT (16) receives these information and searches a data key from a DPMEM (17) by an indirect retrieving method and reads the data key. Plural data keys updated every predetermined period are non-synchronously written to the DPMEM (17). This writing operation is inhibited when the writing and reading operations of the DPMEM (17) are performed in the same timing and the same address. Thus, memory control of the DPMEM (17) can be easily performed. Accordingly, all decryption processings can be completed in real time on a reception side.