PURPOSE: To reduce power consumption and a calorific value without impairing a function by comparing held data outputted from a data holding means with input data, and stopping the input of a clock signal to the data holding means when coincidence is obtained between them.

CONSTITUTION: The data holding means 1 holds the input data by fetching synchronizing with the clock signal inputted via a clock signal stopping means 3, and also, outputs the held data. A comparison means 2 compares the held data outputted from the means 1 with the input data, and outputs a coincidence signal to the means 3 when they are equal, and the means 3 stops the input of the clock signal to the means 1. In other words, no input data is fetched newly and held when the input data remains unchanged. Thereby, it is possible to reduce the power consumption and the calorific value according to that without impairing the function.