In order to maintain accuracy of measurement, a temperature-insensitive electro-optic probe has a laser diode provided to emit a laser beam based on a control signal of an oscilloscope body, a collimator lens provided to convert the laser beam into a parallel beam; an electro-optic element having on an end face thereof a reflective coating, with the optical characteristics which are changed by propagating an electrical field via a metal pin provided at the end face on the reflective coating side, an isolator provided between the collimator lens and the electro-optic element, and adapted to transmit the laser beam emitted from the laser diode, in order to separate a light reflected by the reflective coating from the laser beam, a photodiode provided to convert the reflected light separated by the isolator into an electrical signal, a temperature detection section arranged to be in contact with optical components consisting the isolator, and to detect the temperature of the optical components and output the result of the detection, a temperature adjustment section arranged to be in contact with the laser diode, and to adjust the temperature of the laser diode based on the result of the temperature detection, and a temperature control unit provided to control the temperature adjustment section based on the result of the temperature detection.