[en] A balloon borne hard X-ray experiment operating in the range 15-150 keV with a large sensitive area, high spectral resolution and fine imaging capability has been developed at IAS and AIT Institutes and successfully flown the August 5th, 1985 from the stratospheric balloon Base of Trapani-Milo (Sicily, Italy). During the flight that lasted about 18 hours at an atmospheric depth of less than 3.5 g/cm/sup 2/ pointed observations were performed on the following sources: AO535+26, Crab, MCG 8-11-11 and NGC 4151. In addition several more sources were observed in a scanning mode. In this paper we describe the instrumental configuration and present the pre-flight calibration as well as the in-flight performance