A stroke safety device for a key duplicating machine has a fixed mount and a movable mount. The fixed mount is mounted around a connecting shaft of the key duplicating machine and has a first body, multiple first resilient members, multiple pressing elements, and an adjusting element. The first body has a through hole, an inclined segment, and a mounting recess. The movable mount is pivotally connected to the fixed mount and has a second body and an operating element. The second body is pivotally mounted on a base of the key duplicating machine to cover the inclined segment, and has two opposite side segments. The abutting rod is inserted into the mounting recess of the first body to selectively abut against the adjusting element.