1. An operation-processing device for performing operation processing based on an arbitrary operation program, said device comprising: a register array having plural registers each for holding an arbitrary value based on a write address and a write control signal and outputting this value based on a read address; an operation portion for performing operation on a value read from said register array; an instruction-decoding portion for decoding an operation instruction from an operation program for operating said operation portion; and an instruction-execution-controlling portion for controlling said register array and the operation portion in order to execute an operation instruction decoded by said instruction-decoding portion, wherein said instruction-execution-controlling portion selects one of said registers based on said operation instruction; and wherein based on a value held by said selected register, said instruction-execution-controlling portion performs register-to-register addressing processing for selecting another register.