1. A biological imaging device comprising: a sample holder for holding a biological sample placed thereon; a two-dimensional detector for detecting an image of light emitted from the sample placed on the sample holder; optical waveguide paths for observing the sample placed on the sample holder from two or more directions and for guiding images of light emitted from the sample in different directions to the two-dimensional detector, the optical waveguide paths being provided in different directions; and a main imaging lens arranged between the two-dimensional detector and the optical waveguide paths for forming images guided by the optical waveguide paths at different positions on the two-dimensional detector according to an observation direction, wherein at least one of the optical waveguide paths is an optical waveguide path not receiving direct light from the sample, and the optical waveguide path(s) not receiving direct light from the sample includes an optical element arranged to form an image of the sample within a substantial focus range of the main imaging lens and to allow light beams from the image to travel toward the main imaging lens, and the optical element is an optical element that forms a real image as the image, so that the main imaging lens simultaneously forms images observed from two or more directions and guided by the optical waveguide paths on the two-dimensional detector.