27a bears on the lever pin 26 so that the starting shaft 21 is rotated counterclockwise against the force of the spring 25 when the cam 27c of the starting plate 27 comes in contact with the inclined surface of the retaining arm 39a it moves the retaining arm 39a and after the pin 26 gets over the protrusion 39b the stop lever 27b bears on the tip of the retaining arm 39a now when the starting button 59 is released the pin 26 of the starting shaft 21 which is biased to be rotated clockwise by the spring 25 is locked by the protrusion 39b and cannot be returned the bell crank 39 is also biased to be rotated clockwise by the spring 38 and the arm 39c comes in contact with the flat portion of the cam 37 in this way when the starting shaft 21 is rotated through a predetermined angle the passage 20 is communicated with the valve chamber 65 and the plunger 6 is biased by the force of the spring 63 into the notched cam 21a of the starting shaft 21 whereby the valve body 6a is moved away from the o ring 61 to a retracted.