The invention relates to a computer mouse which is one kind of coordinate input devices for a computer, and more particularly to a computer mouse which is suitably used for a portable computer. The mouse has: a thin mouse case in which an upper face portion opposing a palm when the mouse is used is formed into a downward-concaved shape; and a plate-like member having a shape which extends along the downward-concaved upper face of the mouse case, and the plate-like member is attachable to the downward-concaved upper face of the mouse case in both an upward-convex direction and a downward-concave direction. When the mouse is to be used, the plate-like member is attached in the upward-convex manner to the downward-concaved upper face of the mouse case, and, when the mouse is to be carried, the plate-like member is attached in the downward-concave manner to the downward-concaved upper face of the mouse case, thereby realizing compaction of the mouse in which the original shape and size of the mouse are reproducible.