A processing apparatus includes a chamber main body; a stage having therein a first passage for coolant and a space communicating with the first passage; a first pipeline having a first end portion inserted into the space to be connected to the first passage and a second end portion connected to a coolant supply mechanism; and a first sealing member provided at a gap between a wall surface confining the space and the first end portion. A second passage having one end and the other end is formed within the stage. The one end of the second passage is connected to the gap. The first sealing member is contacted with the wall surface at a side of the first passage with respect to the second passage. The processing apparatus comprises a second pipeline connected to the other end thereof; and a detecting device connected to the second pipeline.