PURPOSE: To obtain an aquarium enabling the observation of aquatic organisms crawling in a granular layer and giving excellent impression by using a light- transmitting granular layer and illuminating the space in the aquarium from below.

CONSTITUTION: Transparent granules such as glass beads or acrylic resin beads are scattered on the bottom of an aquarium 10 having a transparent or translucent bottom plate 11 to form a granular layer 15. An illumination tool 14 is placed under the main body of the aquarium and the inside of the aquarium 10 is illuminated by the light transmitting through the granular layer 15. Since the granular layer 15 has light-transmitting property, the water layer 16 is illuminated by a soft light and the motion of an aquatic organism hiding in the granular layer 15 can be observed. Furthermore, the inside of the aquarium 10 can be observed from above because the aquarium is illuminated from below.