A surgical knife safety device having a handle, a blade connected to the handle, and a guard carried by the handle for sliding movement between a retracted position in which the blade is exposed for use, and an extended position for covering the sharp cutting edge of the blade. In the retracted position, an enlarged guard radius is provided at the distal end of the handle to allow improved handle control and blade orientation. The enlarged guard radius is positioned to allow the user to firmly grip a large distal handle portion which is preferably molded as a single piece with the blade holder, preventing unwanted blade or handle movement due to guard mechanism tolerances. A spring, such as leaf spring, and a pair of detents or slots are provided to fix the guard in the extended or retracted position, and provide resistance during movement between the two positions. Additionally, an antitravel mechanism is incorporated in the guard to prevent accidental retraction from the fully extended position.