A locating device includes a guiding member, a sliding member and a pulling assembly. The guiding member includes a guiding channel inwardly cut through a top thereof, and the sliding member has side plates which each has a locating part. The pulling assembly comprises a pulling body having a guiding element, a fastening element disposed on a side thereof opposite to the guiding element. When the pulling body is in an open state, the fastening element is not located on the locating part; when the pulling body performs a locking operation, the guiding element is slid in the guiding channel and the sliding member is simultaneously slid in another direction opposite to the guiding element; when the pulling body is in a locked state, the fastening element is located on the locating part. Therefore, operational difficulty can be reduced and assembly speed can be improved.