To provide an antenna unit being applied to an active phased array antenna, or the like, in which the transmitting/receiving module can function entirely under a desired temperature environment by cooling it through a cooling unit circulating cooling liquid.

The antenna unit comprises a cooling means for executing heat control of a transmitting/receiving module wherein the cooling means branches cooling liquid being supplied to a plurality of branch pipes for feeding the cooling liquid. Each branch pipe is inserted from one end side of the cooling plate of the cooling unit and the other is inserted to the other side of the cooling plate so that a desired temperature can be attained uniformly over the entire surface of the cooling plate of the cooling unit.