An imaging apparatus 1A includes an electron multiplying solid-state image pickup device which has an electron multiplier section for multiplying charge signals generated in respective pixels; a multiplication gain setting part 41 for setting a multiplication gain in the electron multiplier section; a standard deviation calculator 34 for calculating a noise standard deviation of a noise image acquired under a predetermined condition by the image pickup device; a reference standard deviation storage 35 storing a reference standard deviation, and a standard deviation comparator 36 for comparing the noise standard deviation and the reference standard deviation and outputting an obtained comparison result. At the time of gain adjustment, the multiplication gain setting part 41 adjusts the multiplication gain based on the comparison result by the standard deviation comparator 36. Thereby, an imaging apparatus which enables the user's side to easily and accurately re-adjust the multiplication gain of charge signals in the electron multiplying solid-state image pickup device, and a gain adjusting method for the same are realized.