An observation apparatus is provided. An apex angle of a contact prism is inputted by operating an apex angle setting knob of a control panel. A fining angle of the contact prism is inputted by operating a fitting angle setting knob. A control unit determines the amount of correction for astigmatism of a left observation optical system and the amount of correction for astigmatism of a right observation optical system based on a recognized observation magnification and the inputted apex angle. An axial angle for the astigmatism of the left observation optical system and an axial angle for the astigmatism of the right observation optical system are determined based on the inputted fitting angle. Variable cross cylinder lens rotating drive units are controlled to rotate cylinder lenses of each of the right and left observation optical systems, thereby obtaining the determined axial angle and the determined amount of correction.