signal is supplied thereto from the sensors 23 and 25a to 25d which pulse signal is supplied to a counter circuit 37 the counter circuit 37 issues a high level signal for every five pulse signals supplied thereto which high level signal is inverted by an inverting amplifier 38 to a low level signal which is supplied to an and circuit 31 the timing signal from the loom rotating angle sensor 32 is supplied to the and circuit 31 and the counter cirucit 37 at this time only the counter circuit 37 is reset while there is no output signal issued from the and circuit 31 when one of the valve units 9 and 12a to 12d is not operating properly only four pulse signals are supplied to the counter circuit 37 and at the instant that the timing signal p is issued from the loom rotation angle sensor 32 both input signals to the and circuit 31 are at a high level thus the circuit 31 issues a high level signal to a flip flop circuit f6 for lighting the alarm lamp 33 in a modification shown in fig1 alarm lamps 33 may be respectively associated with the piezo electric sensors 23 and 25a to 25d provided to the electro magnetic valve units 9 and 12a to 12d in the present modification to each of the flip flop circuits f1 to f5 are associated an inverting amplifier 38 and circuit 31 and a flip flop circuit f6 shown in fig8 in such a manner that when one of the valve units 9 and 12a to.