To provide a fixing structure of a shelf, which is capable of preventing the shelf on a desk from sliding or falling down by vibration due to earthquakes and the like, easily moving the shelf, and easily changing a layout as well when installing the shelf on the desk to efficiently place OA devices or the like.

A removable cross-shaped member 6 is inserted into an intersection part of a groove 3 provided at a top plate 2 of a desk 1 into a grid shape, a hollow shelf leg 5 is inserted to be engaged with the cross-shaped member 6, the shelf 4 is installed and fixed to the top plate.