In the normal mode, a first voltage-down converter down-converts an external power supply voltage to provide a large, first internal power supply voltage to the peripheral circuitry via a first internal power supply voltage supplying line, and a second voltage-down converter down-converts the external power supply voltage to provide a smaller, second internal power supply voltage to a memory cell array via a second internal power supply voltage supplying line. This allows fast operation and reduction in power consumption. In conducting a burn-in test, an external power supply voltage supplying line is connected to the first and second internal power supply voltage supplying lines. Thus, the first and second internal power supply voltage supplying lines directly receive the external power supply voltage. This allows an effective burn-in test. In a burn-in test, the first and second voltage-down converters are inactivated.