To provide a double sliding sash locking device which is excellent in controllability, has a control lever without obstruction, and does not deteriorate the appearance and design of sashes.

This locking device 11 locks the meeting stiles 5, 6 of a double sliding sash 1 together. The lower sash meeting stile 6 has a control part 12 provided in such a way as to freely slide along its longitudinal direction, a roller 13 journalled to the control part 12, and a bearing part 14 secured to the upper sash meeting stile 5 and to and from which the roller 13 is locked and unlocked by operation of the control part 12; the roller 13 and the bearing part 14 are covered with the control part 12.