A scintillation counter equipped with a PIN silicon photodiode has been developed for the detection of high density electrons of cascade showers which are induced by high energy cosmic rays. This counter, being placed under an iron absorber of 14.5 r.l. in thickness, was tested at Mt. Norikura to detect high energy gamma-ray and hadron induced bursts. The minimum detectable number of shower electrons is found to be about 1.5×10 3 per unit detector of area 0.25 m 2. This lower bound is corresponding to the number of electrons induced by a vertically incident gamma-ray with an energy of 0.8 TeV.