A power-supply voltage sensing device is disclosed, which relates to a technology for detecting a level of an external power-supply voltage during a test mode. The power-supply voltage sensing device includes a reference voltage trimming unit configured to trim a reference voltage in response to a code signal, a power-supply voltage detection unit configured to select one of a power-supply voltage and an external power-supply voltage in response to a test signal, compare the external power-supply voltage with the reference voltage, and output a detection signal according to the result of comparison, and a reference voltage control unit configured to output the code signal in response to the detection signal.