A content transmission device that is connected to a plurality of external devices including a reproduction device reproducing content data, including a transmitting section transmitting content data to the reproduction device, a detecting section detecting the state of each of the plurality of external devices, a parental level determining section determining for the reproduction device a boundary between a parental level on content data the viewing of which is restricted and a parental level on content data the viewing of which is allowed according to the state of each of the plurality of external devices detected by the detecting section, and a control section controlling transmission of content data from the transmitting section based on the relation between the boundary determined by the parental level determining section and a parental level set on content data.