A casing for fixing a plate member includes a casing body having opposite first and second side plates, and a clamping member having a resilient plate disposed on an inner side of the second side plate, at least one abutment arm protruding inwardly from the resilient plate and adapted to abut against a first surface of the plate member, and an engaging piece proximate to the abutment arm and adapted to releasably engage a second surface of the plate member. The first side plate and the resilient plate are respectively adapted to abut against first and second ends of the plate member for clamping therebetween the plate member. The resilient plate is pullable to move the engaging piece away from the second surface of the plate member.