An engine which can easily cool oil within an oil circulation path. The oil circulation path includes an oil reservoir, an oil pump for sucking oil from the oil reservoir so as to pressurize the oil, an oil supplying oil passage conducting the oil from the oil pump to each of lubrication points, and an oil returning oil passage for returning the oil to the oil reservoir from the lubrication points. The cooling fluid path includes a cooling fluid pump, and a cooling fluid passage for supplying the cooling fluid, which conducts the cooling fluid from the cooling fluid pump to the cooling points. The oil passage and the cooling fluid passage come into contact with each other at one or more points of the engine main body so as to be heat exchangeable via a partition wall.