PROBLEM TO BE SOLVED: To provide a disposable cage lid member in which a filter mounting portion is not easily damaged. A cage lid member (100) constituting a breeding cage includes a plate-shaped lid body (100a), the lid body includes a filter attachment portion (110) to which a ventilation filter (101) is attached, and the ventilation filter includes a male screw portion (101b). The filter mounting portion has an insertion hole 111 for inserting the male screw portion of the ventilation filter, and a cut portion 111a is formed at the edge of the insertion hole. [Selection diagram] Fig. 3
