A semiconductor memory device comprises an address terminal through which an address for reading out stored data in a memory array is input, a clock input terminal through which an input clock is input, a data output terminal through which data read out from the memory array in accordance with the address is output, and a clock output terminal through which an output clock synchronous with the input clock is output. The clock output terminal invariably outputs one of a first voltage and a second voltage. Only when valid data is output from the data output terminal, the clock output terminal causes an output voltage to go from the first voltage to the second voltage or from one voltage to the other voltage.