An unbalanced multiplexer and a scan flip-flop including the unbalanced multiplexer, wherein the unbalanced multiplexer includes a first transmission circuit transmitting a first input signal to an output terminal according to a logic state of a selection signal; and a second transmission circuit transmitting a second input signal to the output terminal according to the logic state of the selection signal. A delay characteristic of a first transmission path from a first input terminal to the output terminal along which the first input signal of the first transmission circuit is transmitted, and a delay characteristic of a second transmission path from a second input terminal to the output terminal along which the second input signal of the second transmission circuit is transmitted, are set differently.