A rain hat device for heavy construction equipment which is installed adjacent to an exhaust gas discharging port of a distal end portion of an exhaust pipe to prevent inflow of rainwater therein, the rain hat device comprising: a mounting bracket having a fixing shaft which is installed on an upper portion of the exhaust gas discharging port of the distal end portion of the exhaust pipe, the mounting bracket fixing the fixing shaft at a position higher than the distal end portion of the exhaust pipe; wherein the mounting bracket is fixed to on e side of an engine room; and a swing cover having a cover support portion connected to the fixing shaft and extending between the fixing shaft and the exhaust gas discharging port, and a weight portion, in which the cover support portion is rotated around the fixing shaft by pressure of exhaust gas discharged from the distal end portion; characterized in that the swing cover is installed on an upper portion of the exhaust gas discharging port in a floating state by the cover support portion so that the swing cover is spaced apart from the distal end portion of the exhaust pipe when the exhaust gas is not discharged from the exhaust gas discharging port, and so that - a weight center is positioned between the fixing shaft and the exhaust gas discharging port when the discharging pressure of the exhaust gas is generated, or - a weight center is positioned between support columns (36a, 36b) supporting both distal ends of the fixing shaft when the exhaust gas is not discharged from the exhaust gas discharging port. a mounting bracket having a fixing shaft which is installed on an upper portion of the exhaust gas discharging port of the distal end portion of the exhaust pipe, the mounting bracket fixing the fixing shaft at a position higher than the distal end portion of the exhaust pipe; wherein the mounting bracket is fixed to on e side of an engine room; and a swing cover having a cover support portion connected to the fixing shaft and extending between the fixing shaft and the exhaust gas discharging port, and a weight portion, in which the cover support portion is rotated around the fixing shaft by pressure of exhaust gas discharged from the distal end portion; characterized in that the swing cover is installed on an upper portion of the exhaust gas discharging port in a floating state by the cover support portion so that the swing cover is spaced apart from the distal end portion of the exhaust pipe when the exhaust gas is not discharged from the exhaust gas discharging port, and so that - a weight center is positioned between the fixing shaft and the exhaust gas discharging port when the discharging pressure of the exhaust gas is generated, or - a weight center is positioned between support columns (36a, 36b) supporting both distal ends of the fixing shaft when the exhaust gas is not discharged from the exhaust gas discharging port. - a weight center is positioned between the fixing shaft and the exhaust gas discharging port when the discharging pressure of the exhaust gas is generated, or - a weight center is positioned between support columns (36a, 36b) supporting both distal ends of the fixing shaft when the exhaust gas is not discharged from the exhaust gas discharging port.