A capotasto to be detachably attached to a neck of a stringed instrument to press strings of the stringed instrument onto a surface of the neck, the capotasto comprising: a clamp including a supporting bar and a string pressing bar for holding the neck therebetween, the supporting bar configured to be arranged at a back surface side of the neck, the string pressing bar configured to be arranged at a surface side of the neck and having a string pressing part provided at its neck facing surface, the supporting bar and the string pressing bar being openably and closeably supported via an opening and closing shaft that are mounted to one of the ends thereof, the supporting bar and the string pressing bar having an opening therebetween at the other of the ends thereof in a closed condition; an opening-direction urging member provided to the clamp and urging in a direction to open the clamp; and a clamp opening-and-closing member arranged in a side opposite to the opening of the clamp, the clamp opening-and-closing member elastically engaging with the supporting bar and with the string pressing bar and being slidable on the supporting bar and on the string pressing bar approximately along a width direction of the neck in a condition in which the clamp clamps the neck, characterized in that the supporting bar has a guide groove that extends in a slightly curved form, and the string pressing bar has a guide groove that extends in a slightly curved form, wherein an engaging part for engaging with the guide groove of the supporting bar is provided at an end of the clamp opening-and-closing member, and an engaging part for engaging with the guide groove of the string pressing bar is provided at the other end of the clamp opening-and-closing member, when being slid in a direction approaching the opening and closing shaft, the clamp opening-and-closing member closes the clamp against an urging force of the opening-direction urging member and enables clamping of the neck and allowing the string pressing part to continue pressing the surface of the neck, and when being slid in a direction away from the opening and closing shaft, the clamp opening-and-closing member allows the clamp to open by the urging force of the opening-direction urging member. a clamp including a supporting bar and a string pressing bar for holding the neck therebetween, the supporting bar configured to be arranged at a back surface side of the neck, the string pressing bar configured to be arranged at a surface side of the neck and having a string pressing part provided at its neck facing surface, the supporting bar and the string pressing bar being openably and closeably supported via an opening and closing shaft that are mounted to one of the ends thereof, the supporting bar and the string pressing bar having an opening therebetween at the other of the ends thereof in a closed condition; an opening-direction urging member provided to the clamp and urging in a direction to open the clamp; and a clamp opening-and-closing member arranged in a side opposite to the opening of the clamp, the clamp opening-and-closing member elastically engaging with the supporting bar and with the string pressing bar and being slidable on the supporting bar and on the string pressing bar approximately along a width direction of the neck in a condition in which the clamp clamps the neck, the supporting bar has a guide groove that extends in a slightly curved form, and the string pressing bar has a guide groove that extends in a slightly curved form, wherein an engaging part for engaging with the guide groove of the supporting bar is provided at an end of the clamp opening-and-closing member, and an engaging part for engaging with the guide groove of the string pressing bar is provided at the other end of the clamp opening-and-closing member, when being slid in a direction approaching the opening and closing shaft, the clamp opening-and-closing member closes the clamp against an urging force of the opening-direction urging member and enables clamping of the neck and allowing the string pressing part to continue pressing the surface of the neck, and when being slid in a direction away from the opening and closing shaft, the clamp opening-and-closing member allows the clamp to open by the urging force of the opening-direction urging member.