A variable focal length lens apparatus includes a lens system where a refractive index changes in response to an input drive signal; a field lens arranged on the same optical axis as the lens system; an image detector detecting an image of a measured object through the lens system and the field lens; a pulse illuminator providing pulse illumination of the measured object based on an input light emission signal; a temperature sensor detecting temperature information for an interior of the lens system; and a controller outputting the drive signal and the light emission signal in addition to correcting the timing of the light emission signal based on the temperature information.