1. A parallel processor for processing a plurality of operation instructions in one cycle in parallel, comprising: a first operation processor; and at least one second operation processor, the first operation processor including, an operation mode retaining unit for retaining an operation mode indicating whether or not the second operation processor should be run in parallel to carry out an operation instruction, wherein the operation mode has a first operation mode in which the first operation processor alone is operated, and a second operation mode in which both of the first operation processor and the second operation processor are operated, a control unit for, in case that the operation mode is the first operation mode, in accordance with the operation mode, supplying the first operation processor with an instruction sequence that defines an operation of the first operation processor, and for generating a control signal to halt an operation of the second operation processor and supplying the control signal to the second operation processor, whereby as to an instruction of the first operation mode, the second operation processor is not operated without embedding an instruction that defines an operation of the second operation processor in the instruction sequence retained in an instruction memory, and an instruction execution unit for switching the operation mode in accordance with an input decoded instruction.