1. A method of task assignment with respect to a plurality of processors comprising a plurality of execution units that execute tasks, a voltage sensor for sensing a voltage of each execution unit, and a voltage controller for maintaining the voltages of the execution units at the same level based on the voltage of each execution unit sensed by the voltage sensor, the method comprising calculating utility difference values between the execution units in each processor and outputting a highest difference value; comparing a utility of a task with the output highest difference value; designating the task to be assigned to the execution unit having the lowest utility in a processor in which the highest difference value is generated when the utility of the task is less than or equal to the output highest difference value as a result of the comparison; repeating the calculating, comparing, and designating with respect to every task; and assigning the tasks to the designated execution units.