A semiconductor integrated circuit includes a plurality of functional blocks, each of which starts and stops an operation thereof in response to assertion and negation, respectively, of a corresponding command signal, a clock generation circuit which generates a clock signal, a clock control circuit which starts supplying the clock signal to each of the functional blocks in response to the assertion of the corresponding command signal, and stops supplying the clock signal to each of the functional blocks in response to the negation of the corresponding command signal.