The cage for breeding small animals according to the present invention comprises a casing with an opening on an upper surface thereof, and a lid for covering the opening of the casing. The lid comprises a frame body attached to an upper end edge of the casing, and an opening for a water supply apparatus to which the water supply apparatus is attached in an openable and closable fashion. A partition board is placed in the casing to divide the housing section within the casing into two. A ventilation section is provided in the partition board, for ventilation between one room and the other room of the divided housing section in the casing. A communicating section for placing a tip of a nozzle of the water supply apparatus is provided by cutting out the partition board.
