PURPOSE: To provide a fluid temperature controller having few component, compact, having a low cost, having good maintenance performance, and able to control the fluid temperature at high precision in a device for controlling the fluid temperature such as coolant or lubricating oil for a heat engine or an air conditioner such as an engine or a gas turbine.

CONSTITUTION: The openings of fluid inflow/outflow ports 9, 10 are adjusted by a rotational valve body 2 to be rotated by extension/contraction of two kinds of springs 3, 4 having different temperature properties of spring constant, and the deflection difference is generated on two springs 3, 4 when the fluid temperature is changed, and the rotational valve body 2 is turned in proportion to this deflection difference, thereby the openings of the fluid inflow/outflow ports 9, 10 are adjusted.