A compact and energy-efficient polluting gas desulfurization apparatus which reduces gas flow pressure loss and the consumption of electrical power. A drum is rotationally supported at its radial center by a horizontal shaft within a fixed duct having a gas inlet port at one end and a gas outlet port at the other end. The right and left sides of the drum and its circumferential surface are lattice-like structures, and the internal space of the drum is filled with gas-liquid contact filler pieces. A slurry holding tank is disposed beneath the rotating drum. Slurry, which is pumped upward by a circulation system, is discharged onto the top of the circumferential surface of the drum at a point offset from the horizontal shaft along the radial axis, thus forming a mechanism able to rotate the drum from the weight of the slurry only and thus eliminating the need for an electric motor.