Disclosed is an observation apparatus capable of eliminating in a suitable manner astigmatism and chromatic aberration generated in an observed image. The apex angle .theta. of a contact prism is input by operating an apex angle setting knob of a control panel, and the attachment angle thereof is input by operating an attachment angle setting knob. Based on the observation magnification recognized and the input apex angle .theta., a control device determines the astigmatism correction amount for a left observation optical system and determines the astigmatism correction amount for the right observation optical system. Further, based on the input attachment angle, the axial angles of the astigmatisms of the left observation optical system and the right observation optical system are determined. Next, variable cross cylinder lens rotation drive devices are respectively controlled to rotate the respective cylinder lenses of the left and right observation optical systems to achieve the axial angle and correction amount as determined.