To provide a strike for sliding door lock capable of stably providing the longitudinal adjusting function of a strike plate at a low cost.

In this strike for sliding door lock 1, both ends of a first adjusting screw 31 are supported by support holes 71b and 72b provided in an inner case 7 housed in an outer case 2b. A female thread 93a provided on the deep part 93 of the strike plate is screwed to the male thread 31b of the first adjusting screw 31. A backup member 11 having a through hole 11b for passing the first adjusting screw 31 is arranged adjacently to the center part 92 of the strike plate. Since the backup member 11 backs up the center part 92 of the strike plate when a force is applied in the direction of opening a sliding door in the state where the hook 101 of the sliding door lock is engaged with the front part 91 of the strike plate, the bending moment generated in the strike plate 9 is minimized.