excavating apparatus 1 b and the points of difference from the other embodiments refer now to fig1 in addition to the center piston case member 22 a mentioned above the excavating bit member 2 is provided with the five peripheral piston case members 22 b furthermore with regard to the center piston case member 22 a and the other five peripheral piston case members 22 b the lengths of piston case main bodies 220 a 220 b differ and the sizes of the pistons 61 61 b housed in the piston case main bodies 220 a 220 b also differ namely the length in the longitudinal directions of the piston case main body 220 b of the peripheral piston case member 22 b shown in for example fig1 b is shorter than that of the piston case main body 220 a of the center piston case member 22 a shown in fig1 a namely a distance l 2 from the air distributor 64 to the bit 42 a shown in fig1 b is shorter than a distance l 1 from the air distributor 64 to the bit 41 shown in fig1 a furthermore corresponding to the length of the piston case main body 220 b the length in the longitudinal directions of the piston 61 b of the peripheral piston case.