Lockback folding knife with safety mechanism

A lockback folding knife, comprising:

• a handle, having a first pivot pin inserted through an end thereof;
• a blade body, having an end distal to a tip thereof and pivotally connected in the handle by the first pivot pin;
• a constraint member pivotally connected with the handle by a second pivot pin, and said constraint member having an end extended to a peripheral edge of the blade body adjacent to the first pivot pin, and an other end extended towards an other end of the handle;
• a first elastic element having an end attached to the handle and other end abutted with the other end of the constraint member, wherein the first elastic element is configured to make the end of the constraint member be abutted with the peripheral edge of the blade body adjacent to the first pivot pin when the blade body is completely stretched out of the handle or received into the handle;
• a locking pin protruded from the constraint member and adjacent to the end of the constraint member;
• a safety switch having an end pivotally connected in the handle and other end exposed out of the handle, said safety switch having a locking groove formed thereon and located correspondingly to the locking pin, wherein the locking groove and the locking pin are engaged when the blade body is completely stretched out of the handle or received into the handle, so as to constrain the blade body in a safety status of being completely stretched out of the handle or received into the handle, and wherein the locking groove is escaped from the safety status of being engaged with the locking pin when a force is applied to the other end of the safety switch, so as to release the blade body;
• and
• a second elastic element having an end attached to the handle and other end abutted the safety switch, wherein the second elastic element is configured to force the locking groove to automatically engage the locking pin when the blade body is completely stretched out of the handle or received in the handle.