A 3-D observation apparatus and 3-D observation system, as well as another observation apparatus, are provided such that it is possible to make observations while substantially in the same posture, without glasses, of either a plurality of 3-D images, or of a 2-D image and a 3-D image. Bright images are provided, there is great freedom in the position at which observations can be made, no distortion of the images is created even if the observer changes his position, and observations can be made with a comfortable observation posture.