The present invention relates to an electro-optic sampling oscilloscope which carries out measurement of a measured signal using an optical pulse generated based on a timing signal from a timing generation circuit. The timing generation circuit includes a frequency measurement circuit which generates a gate signal for a gate interval which is a specified multiple N of the cycle of the desired sampling rate, and counts the input trigger signals during the gate interval of the gate signal; a division circuit which divides the count value of said frequency measurement circuit by the specified multiple N, and determines a divider ratio; and a frequency divider which divides the trigger signals by the divider ratio determined by the division circuit, and outputs the result as the timing signal.