Provided is an optical control element including a lithium niobate substrate, optical waveguides formed on the substrate, and electrodes for controlling light waves propagating through the optical waveguide, in which a temperature control element for substrate for controlling the temperature of the substrate is provided, and the temperature of the substrate is controlled using the temperature control element for substrate to be maintained at a temperature that is equal to or higher than a predetermined lower limit of temperature at which generation of a photo-refractive effect due to light propagating through the optical waveguide is suppressed and is equal to or lower than 80° C.