When a exposure controlling unit changes an aperture value of a diaphragm in a predetermined range, the exposure controlling unit also changes a transmittance of a variable ND filter so as to perform an exposure control and, after obtaining a proper exposure by changing both the aperture value and the transmittance, sets the aperture value after exposure control to Fa, and in a case where the aperture value at which a maximum resolving power is obtained is set to Fb, when a condition, Fa≠Fb, is satisfied and the transmittance is neither the minimum nor the maximum, the exposure controlling unit brings the aperture value close to Fb and changes the transmittance so as to maintain the proper exposure after the exposure control.