A combustion engine comprising a supercharger and a transmission, wherein the supercharger comprises: an impeller configured to pressurize intake air for the combustion engine; an impeller housing configured to cover the impeller; a supercharger rotation shaft to which the impeller is fixed; a supercharger case configured to support the supercharger rotation shaft; a supercharger lubricating fluid passage formed inside the supercharger case, and configured to guide a lubricating fluid for the combustion engine to a portion-to-be-lubricated of the supercharger, the lubricating fluid lubricating portions-to-be-lubricated in the transmission of the combustion engine; and an oil filter disposed in the supercharger lubricating fluid passage, and configured to remove foreign matter from the lubricating fluid, the oil filter being detachably mounted on the supercharger case, wherein the oil filter includes: a filter portion that removes the foreign matter from the lubricating fluid; a mounting portion having an external thread to be screwed into an internal thread formed in the supercharger case; and an operation portion exposed to the outside of the supercharger case, with which a tool for attachment/detachment is engaged, wherein the mounting portion also serves as a sealing portion that seals the supercharger lubricating fluid passage, the supercharger lubricating fluid passage includes a first passage that extends in parallel to a fastening direction of the mounting portion, and a second passage that extends in a direction intersecting the fastening direction and is connected to the first passage, the filter portion is disposed at a connecting portion between the first passage and the second passage, the supercharger is detachably mounted on the combustion engine, the second passage of the supercharger lubricating fluid passage is directly connected with an exit port of a combustion engine lubricating fluid passage defined within an engine case of the combustion engine, by mounting the supercharger case on the engine case, and the exit port of the combustion engine lubricating fluid passage is formed at an abutting surface of the crankcase which abuts the supercharger case. an impeller configured to pressurize intake air for the combustion engine; an impeller housing configured to cover the impeller; a supercharger rotation shaft to which the impeller is fixed; a supercharger case configured to support the supercharger rotation shaft; a supercharger lubricating fluid passage formed inside the supercharger case, and configured to guide a lubricating fluid for the combustion engine to a portion-to-be-lubricated of the supercharger, the lubricating fluid lubricating portions-to-be-lubricated in the transmission of the combustion engine; and an oil filter disposed in the supercharger lubricating fluid passage, and configured to remove foreign matter from the lubricating fluid, the oil filter being detachably mounted on the supercharger case, a filter portion that removes the foreign matter from the lubricating fluid; a mounting portion having an external thread to be screwed into an internal thread formed in the supercharger case; and an operation portion exposed to the outside of the supercharger case, with which a tool for attachment/detachment is engaged,