An active knee bolster and a knee bolster, whose accommodated positions are different, are mounted within an instrument panel along a curved configuration of a wall portion of the instrument panel which, in a vehicle transverse direction, is convex and concave in a vehicle body longitudinal direction. The probes may include both gamma and beta detecting components as well as means for enhancing the accuracy and sensitivity of the beta detectors. With such blower tube arrangement, air pressure is effectively used for stretching the material outwardly and neatly so as to prevent the same from curling, and also for automatically feeding the material toward the sewing machine.