A depth data detection apparatus and monitoring apparatus are disclosed. The depth data detection apparatus has at least two infrared light generators (11, 12) alternately operating, thereby ensuring that each of the infrared light generators has a sufficient power-off time while ensuring continuous operation of the system, so that each infrared light generator can reach its service lift as much as possible. Different infrared light generators can project infrared beams with different angles and/or from different positions, and the depth information obtained can be fused with each other in order to acquire the depth information of the object to be measured more completely. In addition, different infrared light generators can also project infrared beams to different areas or the same area of the space to be measured for their respective purposes.