To perform both synchronous lock releasing operation in sliding devices for main and sub sides and single sliding with the separate lock releasing operation.

A pair of engaging pieces 70, 72 in the main and sub sides to be arranged in a substantially vertical direction when main seats 14, 16 and a sub seat 12 are arranged in parallel are provided to integrally rotate with each lock releasing lever 60 (F, S), 62 in the main and sub sides. An engaging direction of the main side engaging piece 70 with respect to the sub side engaging piece 72 is matched to a lock releasing direction by the main side lock releasing lever 60 (F, S), and the sub side engaging piece 72 is made to be in a through guide shape to overlap and pass through the main side engaging piece 70.