To provide an oil cooler capable of reducing the number of components and assembling processes of the oil cooler, and simplifying a structure, and capable of improving the assembling workability of the oil cooler itself, and the assembling workability of the oil cooler and a radiator tank while facilitating the piping work of a port and the connection pipe side of the oil cooler.

A plurality of shells 1 formed with oil passages are laminated to form a heat exchanger core 2. A connector 3 is arranged at one side of the heat exchanger core 2. An input/output port 4 formed with a first passage R1 and a second passage R2 is formed in the connector 3. The first passage R1 is made to communicate with a communication passage 7a (an oil inlet side passage) of the heat exchanger core 2. The second passage R2 is made to communicate with a communication passage 7b (an oil outlet side passage) of the heat exchanger core 2.