Overload protection equipment protects machinery by disconnecting input and output during overloading instantaneously. It detects an overload reliably and disconnects input and output by detaching the drive key from the groove. When an overload is removed, they are connected automatically with the same torque and indexing position set previously. Torque is set by the built-in torque spring. No fine control is required. It can be also used with both two-shaft butting and wrapping as a flexible coupling. Drive key power transmission allows use in oil.