A plasma treatment apparatus includes a treatment chamber 2 and a gas supply device 30 for supplying a treatment gas into the treatment chamber 2. The gas supply device 30 includes: a mass flow controller box 40 having an intake port 41 and an exhaust port 42; a plurality of pipes 43 to each of which a mass flow controller (43a) is attached; and a plurality of pipes 52 which are connected to the pipes 43 in the mass flow controller box 40 and connected to a plurality of pipes 54 as supply sources of the treatment gas by a plurality of joints 53 outside the mass flow controller box. At least one of the joints 53 is covered by a pipe cover 60 so that the joint 53 is hermetically sealed. The inside of the pipe cover 60 and the inside of the mass flow controller box 40 are communicated by a communicating member (circumferential pipe 61, tube 62).