To form an axial turbine 1 for an exhaust driven super-charger so that the debris of a broken turbine disc do not scatters out from a turbine casing at a very high circumferential speed.

An outside wall 10 of an exhaust diffuser is formed by radially installing an outside contour part 11 and an inside contour 12 in the range in the axial direction of a turbine disc 7, an annular supporting wall part 13 is installed between the both contour parts, the outside contour part of the exhaust diffuser outside wall is formed into an annular expanding member expanding beyond the axial range of the turbine disc, a covering ring 19 for the turbine disc and a moving blade 8 is arranged between a supporting wall part and an outside wall inside contour part of the exhaust diffuser, and an entrance chamber and an exhaust chamber of the turbine are connected with each other so as to locate covering a central plane 23 of the turbine disc in the radial direction of the gas inlet side wall of the turbine exhaust chamber.