the link mechanism and a tube guide portion 16 which is arranged on both end sides of the water supply pump 5 and which protects the water supply tube 13 at an unspecified portion of the pump cover 14 upon opening and closing the pump cover 14 here upon opening and closing the pump cover 14 the opening and closing detecting means detects the opening and closing operation of the pump cover 14 via the link mechanism not shown and outputs a detection result to the control portion 2 b in accordance therewith the control portion 2 b recognizes the opening and closing operation of the pump cover 14 the tube guide 16 is arranged on both end sides of the water supply pump 5 and thus the water supply tube 13 is accommodated in an inner groove of the tube guide 16 and maintains its proper position for supplying the water consequently upon opening and closing the pump cover 14 it is possible to prevent the damage of the water supply tube 13 due to the sandwiching thereof by the unspecified portion of the pump cover 14 as mentioned above according to the first embodiment water supply means for cooling the probe 10 is provided on the other hand a hollow.