An optical instrument of the present invention comprises a ring member which is arranged to be rotatable with respect to a lens barrel, and also to slide in an optical axis direction, a movement mechanism for slide movement of the ring member to a first position or a second position in the optical axis direction, an encoder that generates signals in accordance with a rotation operation of the ring member, a slide position determination section for determining positional change accompanying slide movement to the first position or the second position by the movement mechanism, and a control section for performing determination of the signals from the encoder to switch the display operation, and prohibiting switching of the display operation when the slide position determination section has determined a positional change accompanying the slide operation.