A temperature controller for a gas laser which controls temperatures of temperature-controlled apparatuses including a first temperature-controlled portion requiring a high-precision temperature-control and a second temperature-controlled portion requiring a low-precision temperature-control and allowing a temperature-control with a low or high temperature as compared with the first temperature-controlled portion, comprises a first temperature control portion generating a cooling agent or a heating agent for adjusting a temperature of each first temperature-controlled portion, a second temperature control portion generating a cooling agent or a heating agent for adjusting a temperature of each second temperature-controlled portion, a first piping system connecting the first temperature control portion and each first temperature-controlled portion in parallel, and a second piping system connecting the second temperature control portion and each second temperature-controlled portion in parallel.