An EGR device comprising: a first cooling passage that introduces a flowing medium discharged from an engine into a main radiator so that the flowing medium is cooled therein and then the flowing medium returns to the engine; a second cooling passage that introduces a part of the flowing medium cooled in the first cooling passage to a sub-radiator so that the flowing medium is further cooled therein, the second cooling passage introducing the flowing medium to an EGR cooler to return the flowing medium, which is discharged from the EGR cooler, to the engine; a flow regulating means that is capable of regulating a flow amount of the flowing medium that is cooled in the first cooling passage so as to be introduced into the sub-radiator, characterised in that: the main radiator and the sub-radiator are combined to form a radiator having a tank (20a, 20b) as one unit, in that an inner space of the tank (20a, 20b) of the radiator is separately divided by a partition plate (20c, 20d) that is provided with a communicating hole therein to form the tank of the main radiator and the tank of the sub-radiator, and in that the flow regulating means has a piston type orifice valve including a piston that has an orifice for obtaining a certain opening area relative to an area of the communicating hole of the partition plate (20c, 20d), the piston being able to open and close the orifice, and a driving means that drives the piston. a first cooling passage that introduces a flowing medium discharged from an engine into a main radiator so that the flowing medium is cooled therein and then the flowing medium returns to the engine; a second cooling passage that introduces a part of the flowing medium cooled in the first cooling passage to a sub-radiator so that the flowing medium is further cooled therein, the second cooling passage introducing the flowing medium to an EGR cooler to return the flowing medium, which is discharged from the EGR cooler, to the engine; a flow regulating means that is capable of regulating a flow amount of the flowing medium that is cooled in the first cooling passage so as to be introduced into the sub-radiator, characterised in that: the main radiator and the sub-radiator are combined to form a radiator having a tank (20a, 20b) as one unit, in that an inner space of the tank (20a, 20b) of the radiator is separately divided by a partition plate (20c, 20d) that is provided with a communicating hole therein to form the tank of the main radiator and the tank of the sub-radiator, and in that the flow regulating means has a piston type orifice valve including a piston that has an orifice for obtaining a certain opening area relative to an area of the communicating hole of the partition plate (20c, 20d), the piston being able to open and close the orifice, and a driving means that drives the piston. the main radiator and the sub-radiator are combined to form a radiator having a tank (20a, 20b) as one unit, in that an inner space of the tank (20a, 20b) of the radiator is separately divided by a partition plate (20c, 20d) that is provided with a communicating hole therein to form the tank of the main radiator and the tank of the sub-radiator, and in that the flow regulating means has a piston type orifice valve including a piston that has an orifice for obtaining a certain opening area relative to an area of the communicating hole of the partition plate (20c, 20d), the piston being able to open and close the orifice, and a driving means that drives the piston.