The present invention discloses a mechanical automatic fishing device. The fishing device comprises a fishing rod, a fishing line, a relatively fixed installation seat and a bait-changing apparatus. The fishing line comprises a fishing line upper section and a fishing line lower section which are connected through a first hook and a first hanging ring; and the fishing rod is mounted on the installation seat, and can horizontally and vertically rotate; the bait-changing apparatus comprises a supporting seat, a second notch is formed in the supporting seat, and at least one bait box that can translate in a stepping manner is arranged on the supporting seat; at least one chamber is formed in each bait box; a third notch is formed in the open position of each chamber of each bait box; and when the first hanging ring is placed at the open positions of the chambers of the bait boxes, the first notch of the first hanging ring directly faces the second notch of the bait boxes, and meanwhile the first hook passes through the second notch and the third notch along with the fishing line upper section, the first hook hooks the first hanging ring. Therefore, the mechanical automatic fishing device that is simple in structure, easy to produce, and more convenient and smoother in use is provided.