To provide a dot impact printer in which a ribbon mask can be easily set, detached in a short time while a hammer bank is fixed, and positions of a printing pin and a window hole of the ribbon mask can be determined correctly.

A mold engaging part 6 having a positioning hole 8 and a hook 9 with a projection in a direction of the positioning hole is fixed to each end in a reciprocation direction of a ribbon mask 1. A holder 7 is mounted to each end in a reciprocation direction of a hammer bank 2, which has a positioning projection 11 to be engaged with the positioning hole 8 of the mold engaging part 6 fixed to each end of the ribbon mask 1, a wall part 12 for catching the hook 9 of the mold engaging part 6, and a wall part 13 at a front face of a lower end for pressing a leading end of the mold engaging part 6.