Provided is a substrate treatment apparatus including a process chamber, a supporting unit, a gas supplying unit, and a plasma generating unit. The plasma generating unit may include a power, a primary antenna connected to the power through a first line, a secondary antenna connected to the power through a second line diverging from the first line at a first junction, the primary and secondary antennas being connected in parallel to the power, a third reactance device connected to the power through a third line diverging from the second line at a second junction, the secondary antenna and the third reactance device being connected in parallel to the power, and a variable reactance installed on the second line between the second junction and the secondary antenna.