An intake gas cooling device for a supercharging internal combustion engine, the intake gas cooling device comprising: an intercooler that is provided in an intake gas passage, the intercooler having a low temperature-side tank, and the low temperature-side tank being equipped with a reservoir that is provided at a lower portion of the low temperature-side tank to temporarily accumulate condensed water; an outlet pipe that is connected to the low temperature-side tank; and a water suction pipe that extends from a bottom portion of the reservoir into the outlet pipe and that has a first opening in the outlet pipe, the first opening being suitable to be located upstream of a throttle valve in a flow direction of intake gas, characterized in that a bottom wall of the reservoir descends toward an end portion of the water suction pipe on the reservoir side, a portion of the bottom wall which is located in a vicinity of the end portion forms a lowermost portion of the bottom wall, the low temperature-side tank is vertically partitioned by a partition board into an upper chamber through which intake gas flows and the reservoir, a water drop opening through which condensed water on the partition board is dropped into the reservoir is provided to the partition board, at a lowermost portion of the partition board, a baffle plate is provided on an upper surface of the partition board, the baffle plate is arranged in such a manner as to reduce the speed at which condensed water flowing on the partition board is drained to the outlet pipe when the condensed water overflows onto the partition board, and the upper chamber has a cross-sectional area that is equal to or larger than a cross-sectional area of the outlet pipe, above the baffle plate. an intercooler that is provided in an intake gas passage, the intercooler having a low temperature-side tank, and the low temperature-side tank being equipped with a reservoir that is provided at a lower portion of the low temperature-side tank to temporarily accumulate condensed water; an outlet pipe that is connected to the low temperature-side tank; and a water suction pipe that extends from a bottom portion of the reservoir into the outlet pipe and that has a first opening in the outlet pipe, the first opening being suitable to be located upstream of a throttle valve in a flow direction of intake gas, characterized in that a bottom wall of the reservoir descends toward an end portion of the water suction pipe on the reservoir side, a portion of the bottom wall which is located in a vicinity of the end portion forms a lowermost portion of the bottom wall, the low temperature-side tank is vertically partitioned by a partition board into an upper chamber through which intake gas flows and the reservoir, a water drop opening through which condensed water on the partition board is dropped into the reservoir is provided to the partition board, at a lowermost portion of the partition board, a baffle plate is provided on an upper surface of the partition board, the baffle plate is arranged in such a manner as to reduce the speed at which condensed water flowing on the partition board is drained to the outlet pipe when the condensed water overflows onto the partition board, and the upper chamber has a cross-sectional area that is equal to or larger than a cross-sectional area of the outlet pipe, above the baffle plate.