A scan flip-flop circuit includes an input unit and an output unit. The input unit selects one of a data input signal and a scan input signal depending on an operation mode and generates an intermediate signal based on the selected signal. The output unit generates an output signal based on the intermediate signal and selects one of a data output terminal and a scan output terminal depending on the operation mode to provide the output signal through the selected output terminal. A voltage level at the selected output terminal bidirectionally transitions between a first voltage level and a second voltage level. A voltage level at a non-selected output terminal unidirectionally transitions between the first voltage level and the second voltage level.