1. An operation-processing device for performing operation processing based on an arbitrary operation program, said device comprising: a register array having a plurality of registers each for holding an arbitrary value based on a write address and a write control signal and for outputting the held value to a signal line based on a read address; an operation portion having an input coupled to said signal line independent of an intervening addressable register such that a value read from said register array to said signal line based on a read address is capable of being provided to said input without further addressing a register, the operation portion being operable for performing an operation on said value read from said register array to said signal line; an instruction-decoding portion for decoding an operation instruction from an operation program for operating said operation portion, wherein said operation instruction includes at least one bit indicative of an access method; 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, in the event said at least one bit is indicative of a first access method, then said instruction-execution-controlling portion is operable for (i) selecting one of said registers of the register array based on said operation instruction, and (ii) based on a value held by said selected register, and without reference to a value previously loaded into another register, performing register-to-register addressing processing for selecting another of said registers of said register array; and wherein, in the event said at least one bit is indicative of a second access method, then said instruction-execution-controlling portion is operable for selecting one of said registers based on said operation instruction, and not performing register-to-register addressing processing for selecting, based on a value held by said selected register, another of said registers of said register array.