Provided is a grounding structure for an internal combustion engine, including a resinous body 2 configured to be attached to an engine body 7 and having a recessed portion 6 formed on a side thereof facing the engine body 7; a nut portion 13 integrally provided in the body 2, wherein the nut portion 13 includes a first end portion 13a opened into the recessed portion 6 and is made of a conductive material; and an oil pressure switch 5 configured to be attached to a second end portion 13b of the nut portion 13; and a conductive spring 16 arranged inside the recessed portion 6, wherein the conductive spring 16 is attached to the first end portion 13a of the nut portion 13 and is pressed against the engine body 7.