An observation system includes an observation apparatus including a housing having an arrangement surface for placement of a sample, the sample including a culture medium, and an external illumination unit which is disposed outside the housing and includes at least one light source configured to emit illumination light. At least a part of the arrangement surface is formed of a transparent member having an optically transparent property. The observation apparatus includes an imaging unit which is provided in the housing and includes an image sensor configured to image, via the transparent member, the sample illuminated by the illumination light from the external illumination unit to acquire images of at least three colors.