A position adjustment mechanism for grinding wheels includes a rotating body, a first grinding unit, a second grinding unit, and a fixing nut. The rotating body includes a fixing surface and a first thread portion. The first grinding unit includes a first grinding portion and a fixing portion fixedly engaged with the fixing surface. The second grinding unit includes a second thread portion, which is threadedly engaged with the first thread portion of the rotating body, and a second grinding portion which is spaced from the first grinding portion and which has a different grinding precision from that of the first grinding portion. The fixing nut is threadedly engaged with the first thread portion, and presses axially against the second grinding unit. Thereby, a rough grinding and a fine grinding can be accomplished together within a grinding process, and adjustment on a spacing between the two grinding wheels becomes easy.