An assembly type hydraulic-operating oil cooling apparatus, comprising: a body; a front cap having a cooling water inlet and a cooling water outlet, which are separated from each other by a partition; a cap clogging plate arranged between the front cap and one end of the body; heat exchange pipes arranged inside the body for channeling cooling water from the cooling water inlet to the cooling water outlet, said heat exchange pipes being respectively inserted into heat exchange pipe engaging openings at said clogging plate; an oil inlet and an oil outlet respectively formed at end portions of the body and communicating with said inside of the body; and clogging plates arranged at said inside of the body; characterised in that the body is formed by a desired number of units that are bolt-engaged with each other in series, each unit being formed with engaging holes and body cooling water passageways in circumferential direction thereof; packings are respectively inserted in intermediate portions between neighbouring units in such a manner that projecting portions of said packings alternately confront each other; a further cap clogging plate is arranged between a rear cap and a further end of the body; wherein said heat exchange pipes and support rods are respectively inserted into heat exchange pipe engaging openings and support rod engaging holes of said cap clogging plates, the support rods being further inserted into support rod holes of said clogging plates that are attached to the projecting portions of the packings; and wherein said front cap is formed with cooling water body inlets in radial direction and engaged at one side of the first mentioned cap clogging plate, and said rear cap is formed with cooling water body inlets in radial direction and engaged at one side of said further cap clogging plate, said cooling water body inlets communicating with said body cooling water passageways. a body; a front cap having a cooling water inlet and a cooling water outlet, which are separated from each other by a partition; a cap clogging plate arranged between the front cap and one end of the body; heat exchange pipes arranged inside the body for channeling cooling water from the cooling water inlet to the cooling water outlet, said heat exchange pipes being respectively inserted into heat exchange pipe engaging openings at said clogging plate; an oil inlet and an oil outlet respectively formed at end portions of the body and communicating with said inside of the body; and clogging plates arranged at said inside of the body; characterised in that the body is formed by a desired number of units that are bolt-engaged with each other in series, each unit being formed with engaging holes and body cooling water passageways in circumferential direction thereof; packings are respectively inserted in intermediate portions between neighbouring units in such a manner that projecting portions of said packings alternately confront each other; a further cap clogging plate is arranged between a rear cap and a further end of the body; wherein said heat exchange pipes and support rods are respectively inserted into heat exchange pipe engaging openings and support rod engaging holes of said cap clogging plates, the support rods being further inserted into support rod holes of said clogging plates that are attached to the projecting portions of the packings; and wherein said front cap is formed with cooling water body inlets in radial direction and engaged at one side of the first mentioned cap clogging plate, and said rear cap is formed with cooling water body inlets in radial direction and engaged at one side of said further cap clogging plate, said cooling water body inlets communicating with said body cooling water passageways.