To provide a screwdriver bit and a screw which certainly prevent the occurrence of coming out of the screwdriver bit in screwing work, and can be effectively applied to a plurality of kinds of screw with different dimensions, and a combination of those.

The combination is composed of the screwdriver bit 10 setting each radius direction outer peripheral edge portion 14a of a cross-shaped edge piece 14 and its tilting angle so as to unite a distal end cutting edge portion 12 in a wedge shape at each opening outer peripheral edge portion 23a of a cross-shaped groove portion of a bit fitting groove of the screw; and the screw 20 slightly expanding an opening portion of a screw head rather than M dimensions by Japanese Industrial Standards and the like, configuring the cross-shaped groove portion so as to extend from the opening portion to a bottom portion of required depth at a predetermined tilting angle, and respectively formed with a tapered inner peripheral surface portion 25 contracted to be G dimensions by Japanese Industrial Standards and the like in a stepped shape at a bottom portion side part of each tilting inner peripheral surface portion 24a of the cross-shaped groove portion.