Patent ID: 8491183

Claim:
A detent escapement for a timepiece comprising: an escape wheel; a balance that includes an impulse jewel which can contact a wheel tooth of the escape wheel and an unlocking stone, and that freely oscillates about a balance staff; a blade that includes a locking stone which can contact the wheel tooth of the escape wheel, and that is supported being capable of approaching to and separating from the escape wheel; and a one-side actuating spring that can contact the unlocking stone and be elastically deformed along the approaching and separating direction with respect to the blade, wherein the one-side actuating spring is formed so that a maximum stress portion, which is generated at the time of operating due to the contact of the unlocking stone when the balance is return-rotated, is present to be the side opposite to the balance by a second straight line which is perpendicular to a first straight line which connects the center of the balance staff and fulcrum of the blade, and passes through the fulcrum.