A casing assembly for accommodating a stylus includes a casing and a button. The casing has an accommodation recess and an opening in communication with each other. The accommodation recess has a first end and a second end opposite to each other on a longitudinal axis thereof, and accommodates the stylus. The opening extends from the first end to the second end. The button includes an operation portion and a pushing portion connected to each other. The operation portion is pivotally disposed at the casing so as to be pivotable between an initial position and a released position. The pushing portion is located in the accommodation recess. When the operation portion is pivoted from the initial position to the released position, the pushing portion in the accommodation recess is moved toward the opening so as to push the stylus out of the accommodation recess.