PURPOSE: To attain high speed by deciding the priority depending whether at least 1-bit of logical '1' bit exists in bits constituting m-set of blocks and deciding at which part the initial logical '1' exists among the entire data by the retrieval and data conversion only of bits of one set of block among m-set of split blocks.

CONSTITUTION: A carry generating section 1 splits an input data of 2n×m-bit is split into m-set of blocks comprising 2n-bit in the CMOS circuit constitution to represent at which the data of first logical 1 exists. A priority detection section 2 represents at which order of digit in one set of data specified by the carry generating section 1 the 1st logical 1 data exists. A conversion section 3 calculates at which order of digit the 1st logical '1' data exists among the entire data from the outputs of the carry generating section and the priority detection section and converts the result into a binary data. Thus, the CMOS transistor is in use and the priority encoder operated at a high speed is obtained.