An exhaust gas purifier includes a particulate filter for oxidizing collected particulates, a reversing device that reverses an exhaust gas upstream side and an exhaust gas downstream side of the particulate filter. The particulate filter includes a collecting wall for collecting the particulates, which includes a first collecting surface and a second collecting surface. The first and the second collecting surfaces are alternately used for collecting the particulates by the reversing device. The catalyst device is arranged adjacent to the particulate filter at a position always being at the downstream side of the particulate filter.