Variable focal length lens device and variable focal length lens control method

A variable focal length lens device comprising:

• a liquid resonant liquid lens unit having a refractive index changeable in response to an inputted drive signal;
• a scanning range setter configured to set a predetermined standard frequency band as a scanning range of a frequency of the drive signal;
• a resonance frequency detector configured to cause the frequency of the drive signal to be scanned over the scanning range and detect a resonance frequency of the liquid lens unit based on an oscillation state of the liquid lens unit;
• and
• a resonance frequency estimator configured to calculate an estimated value of a target resonance frequency of the liquid lens unit based on a standard resonance frequency that is a resonance frequency detected from the standard frequency band by the resonance frequency detector, wherein
• the scanning range setter is configured to further set a target frequency band including the estimated value of the target resonance frequency as the scanning range.