close driving means 108 accordingly the outlet open close driving means 108 drives the outlet motor 21 according to the control of the control means 104 so that the outlet motor 21 is driven forward and the pinion 23 coupled with the shaft 22 of the outlet motor 21 is revolved to move the rack 25 coupled therewith downward to thereby lower the outlet door 13 coupled with the rack 25 to open the outlet 7 at this time at step s19 an outlet open close detecting means 110 detects the position of the outlet door 13 which is moved downward by the outlet motor 21 and an inlet open detecting means 114 detects the position of the slide member 33 which is moved upward by the inlet motor 31 accordingly the control means 104 receives signals detected by the outlet open close detecting means 110 and the inlet open detecting means 114 and determines whether the outlet door 13 and the inlet grill 34 are opened or not if the outlet door 13 and the inlet grill 34 are not opened in case of 34 no 34 operation returns to step s17 and the outlet motor 21 and the inlet motor 31 are driven until the outlet door 13 and the inlet grill 34 are opened if the outlet door 13 and the inlet grill 34 are opened in case of 34 yes 34 at step s19 operation proceeds to step s20 at which the outlet open close drive means 108 stops driving the outlet motor 21 according to the control of the control means 104 to conclude the open operation of the outlet door 13 and the inlet open close drive means 112 stops driving the inlet motor 31 according to the open.