To provide a water level adjustment device of a washing machine which can accurately control the level of water by use of a semiconductor type water level sensor that is excellent in the linearity of its output.

This water level adjustment device comprises: a semiconductor type water level sensor 60 made of a semiconductor and sensing the level of water in a washing drum by varying its internal resistance value with the voltage applied; a power supply part 61 supplying power to the semiconductor type water level sensor 60; an amplifying part 70 amplifying the output of the semiconductor type water level sensor 60; a control part 25 judging the level of water from the input of a signal outputted from the amplifying part 70, to control the level of water; a water feed valve driving part 35 opening or closing a water feed valve 34 according to the control signal of the control part 25; a drain valve driving part 45 opening or closing a drain valve 36 according to the control signal of the control part 25; and a washing machine operating part 55 operating a washing machine with the control signal of the control part 25 when the level of water in the drum has reached a set level.