The invention relates to a craftsman knife, which can automatically lock a blade and includes a knife case (1), a blade (2), a knife file (3) and a push cover (4), wherein, a continuous double wedge (12) is arranged on the knife case (1), the knife file (3) is arranged behind the blade (2), an elastic element and a locking piece (6) the head (61) of which is rounded off, are arranged in the knife file (3), the elastic element has the tendency to push the head (61) of the locking piece (6) into a space between the double wedge (12) on the knife case (1), an inclined plane (41) is arranged at the back of the push cover (4) at each side of the head (61) of the corresponding locking piece (6), the two inclined planes (41) are opposite to each other, and can all squeeze the head (61) of the locking piece (6) out of the double wedge (12) on the knife case (1). Compared with the prior art, the invention realizes the locking of the blade relative to the knife case through the joint effect of the elastic element, the locking piece and the inclined plane on the pushing cover, the mutual coordination is firm, thus guaranteeing the quick and effective locking and unlocking of the blade relative to the knife case; furthermore, the parts are arranged in the craftsman knife in a simple way, and is easy to manufacture.