A processor includes a plurality of execution units configured to execute instructions, a pre-decoder configured to sieve out a power-switching instruction from the instructions, and a power controller configured to control the status of the execution unit based on the power-switching instruction. The power controller includes an identification decoder configured to generate identifications respectively corresponding to the execution units from the power-switching instruction, and a power manager configured to switch the execution unit corresponding to the identification. Particularly, the power-switching instruction includes a power-on instruction and a power-off instruction. The processor further includes a plurality of reservation tables each configured to store the instruction to be executed by one of the execution units, and a turn-off signal is not conveyed to the power manager until the reservation table corresponding to the execution unit to be turned off is empty.