A rolled hem switching device comprises a lower knife mounting base which is arranged below a throat plate and is adjustably movable in a lateral direction by way of a laterally moving mechanism provided on a sewing machine frame, a moving pawl which slidably engages a guide groove extending in a cloth feeding direction on a side surface of the lower knife mounting base, a presser member which is fixed to the lower knife mounting base and slidably supports a side surface of the moving pawl and which comprises a horizontal slit of a given length for projecting a projecting portion of the moving pawl therethrough and a lower knife which is fixed to a side surface of the lower knife mounting base at a front side of the presser member for slidably supporting a side surface of the moving pawl. As a result, it is possible not only to switch between forming overlock stitches and forming rolled hem, but also to adjust the width of the overlock stitches by integrally adjusting the lateral positions of the moving pawl and lower knife without changing a throat plate and it is also possible to stably hold the moving pawl.