To provide the automatic expansion mechanism of an active fishhook which is deformed to automatically expand the shape of the points in the mouth of a fish, when bitten by the fish, thus catching the fish by itself.

The fishhook having two corresponding points whose base portions have a common coil-like spring to form an integrated structure is formed. For the first time, the two points are maximally expanded. A ring capable of simultaneously holding both the shank portions and sliding on the shank portions is mounted. The ring is attached to the end of a line penetrated into the wound portion of the coil. First, the two points are compressed to the force of the spring, and the ring is slipped toward the points and then set. When the fishhook is attached to a bait, used for a spinning treatment by a conventional method, and bitten with a fish, the points receive a tension by the escaping force of the fish, and the ring is moved back toward the spring to return the original form by the counteraction of the fishhook. Consequently, the fishhook is automatically expanded.