To solve the following problems: a safety device of a conventional cutting device holds locking of a cutter only when the cutter is opened to an uppermost position, and therefore the cutter is unsafe before reaching the uppermost position; further when the cutting machine is applied to an ordinary paper cutter for cutting only a small amount of paper, canceling operation of the safety device is required, which is inconvenient for the user.

A new safety device of a cutting device is provided with a stepped pin penetrating through a frame and a cutter, and lock canceling operation is carried out prior to upward opening operation of the cutter. According to the structure of the safety device, the canceling operation of the stepped pin is achieved by rotating a screw, and therefore lock cancellation by erroneous operation by the user is avoided. Further by slightly expanding a hole formed in the cutter, the safety device does not require the canceling operation when only a small amount of paper is cut. In this manner the safety and convenience of the safety device are enhanced.