An oil cooler is fixed to an engine via an installation stay provided around an outer periphery of the oil cooler. Thus, the load applied to a core portion is reduced, and the load is dispersed on entire portion of the oil cooler. Thus, the respective stresses applied to respective portions of the oil cooler are very small, and a deformation of the core portion is prevented. Furthermore, since the respective stresses on any portion of the oil cooler is reduced, it is possible to make the oil cooler with aluminum whose strength is lower than that of iron. Furthermore, since the thickness of the installation stay can be reduced, difference in the thermal expansion quantity caused by difference in coefficients of linear expansion of the bolt and the installation stay is significantly reduced, and the loose bolt of the bolt caused by difference in coefficients of linear expansion is prevented.