To provide a simple structure of a seat adjuster and perform slide simultaneous locking on the right and left even at the time of collision on a side face of a vehicle securely by fixing slide locks on the right and left which are hooked and removed on a stopper of anchor rails on the right and left at both ends of a cross beam provided between slide rails on the right and left and fixing an operation lever.

A cross beam 15 is supported on slide rails 13, 14 on the right and left in such a manner that it can rotate by brackets 16, 17 on the right and left. Moreover, slide locks 21 on the right and left are supported at both ends of the cross beam 15 and are hooked and removed on a stopper 19 of anchor rails 11, 12 on the right and left. Furthermore, an operation lever 22 is supported on the cross beam 15 and is elongated on a front side of a seat cushion 31. As a result, it is possible to ensure slide simultaneous locking on the right and left. Moreover, at the time of collision on a side face of a vehicle, horizontal load is transmitted from one rail combination to the other rail combination by the cross beam 15 in the anchor rails 11, 12 on the right and left and the slide rails 13, 14 on the right and left and is dispersed.