Disclosed are an apparatus and method for controlling transmission power of a terminal in a wireless environment. The apparatus for controlling transmission power of a terminal includes an optimal transmission power calculation unit configured to calculate an optimal transmission power value for a terminal of a type, the terminal being accessible to one or more wireless networks; a transmission power setting unit configured to, when an access of the terminal to at least one of the one or more wireless networks is sensed, provide the terminal with optimal transmission power values corresponding to the terminal and the network accessed by the terminal.