To provide a butterfly valve capable of easily controlling a flow rate and pressure by making flow with a quantity of fluid corresponding to an opening angle of a valve element of a butterfly valve as closely as possible fully preventing the fluid from occurring of cavitations and reducing a torque acting in a direction to close the valve element, when the valve element is slightly opened from a full closure state.

A taper surface that gradually gets narrower from one end to a seal face is formed on inner surface of a cylindrical valve body, a width and an inclination of the taper face (a pinching angle between the taper face and the seal face is the reference) are minimum at parts where the width and the inclination are in a direction of extending of the valve shaft and maximum in a direction crossing to the position of extending of the valve shaft and a space between both faces is gradually increased. The valve element having comb teeth type protrusions formed on periphery of the valve element may be shared, and a straightening plate may be also shared.