104 is an inverter the photoelectric tubes 6a and 6b which are of the reflective type each output a signal when detecting the crotch panel 1 thereon the signal from the tube 6a is shaped by the schmitt trigger circuit 101a and the signal from the tube 6b is shaped by the schmitt trigger circuit 101b provided the schmitt trigger circuit 101a has an output waveform as shown in fig1 a and that the schmitt trigger circuit 101b has an output waveform as shown in fig1 c that means the leading end 1a passes on the photoelectric tube 6a at time t 1 and the rear end 1b passes on the photoelectric tube 6b at time t 2 since the signal from the schmitt trigger circuit 101a is directly sent to the one shot multivibrator 102a the one shot multivibrator 102a outputs a signal as shown in fig1 b accordingly the operating valve 103a is operated for the duration of a time constant t 1 starting from time t 1 through which time the air cylinder 56a is expanded whereby the upper blade 54b is pivoted down to cut the folded tape 2 since the signal from the schmitt trigger 101b is reversed by the inverter 104 to be as shown in fig1 d before entering the one shot multivibrator 102b the one shot multivibrator 102b outputs a signal as shown in fig1 e accordingly the operating valve 103b is operated for the duration of t 2 starting from time t 2 through which time the air cylinder 56b is expanded whereby the upper blade 55b is pivoted down to cut the folded tape 2 according to the above construction the folded tape 2 stitched on a series of.