A peg for a stringed instrument having a head and a hole formed in the head includes: a main body which is mounted to the head; a worm gear rotatably provided to the main body and having a knob on an end portion thereof; a worm wheel rotatably supported by the main body and engaging with the worm gear; a winding shaft having an axis, the winding shaft connected to the worm wheel and inserted into the hole of the head in the condition that the main body is mounted to the head; and a ring-shaped guide member penetrated by the winding shaft and fitted into the hole of the head. The guide member is inserted to the main body along the axis of the winding shaft so as to be secured to the main body.