To provide a network device having power saving function by which a mode is converted into a power saving mode to reduce power consumption when the use of all data terminal equipments is stopped for not less than prescribed period and the lowering of the reliability of an operation or durability due to overheat is prevented.

The network device connected to a plurality of ports by data cables so that client PC (10) being data terminal equipment are controlled is provided with signal detection parts (25) detecting the presence or absence of signals on the data cables and a switching power part (26) changing power to an off state when the signaling of all the signal detection parts (25) is stopped for not less than a set time.