A cross-section processing observation apparatus includes an ion beam control unit which controls a charged particle beam generation-focusing portion and a deflector, and a DAC which converts an input digital signal into an analog signal which is to be input to the deflector. A field-of-view setting portion sets a value of a field of view of a charged particle beam where the scanning performed by the deflector is performed on the basis of a set value of a slice amount, and the field-of-view setting portion is configured to set a value of one-nth of the slice amount, where n is a first natural number, as an input digital value “1” of the digital/analog converter and to set a value obtained by multiplying said value set as the input digital value “1” by a second natural number as a value of the field of view.