Each small instruction in a VLIW instruction (long instruction) is added with the number of NOP instructions which succeed the small instruction, and these NOP instructions are deleted from the succeeding long instruction. A plurality of long instructions are therefore time-compressed. Thereafter, a plurality of small instructions in each long instruction are divided into a plurality of groups, and a combination of operation codes (OP codes) of small instructions in each group is replaced by a group code to generate a compressed, grouped instruction. Each long instruction is therefore space-compressed. An instruction expanding unit has an instruction expanding circuit for each grouped instruction. Each instruction expanding circuit expands one grouped instruction in a long instruction, generates a group of small instructions represented by the grouped instruction, and supplies the group of generated small instructions to respective function units via a decode unit. In this case, each instruction expanding circuit supplies after each small instruction NOP instructions same in number as that designated by a NOP number associated with each small instruction in this grouped instruction.