To provide the mounting structure of a built-in device capable of preventing excessive shocks on the built-in device installed in a casing, and an electronic device employing the mounting structure.

A reinforcing member 3 is formed by setting a second space s2 with a casing 2 through an interpolation member 6 in the bottom of the casing 2 equivalent to the installing place of a built-in device 1, an attaching tool 4 extended in a height direction is fixed to the reinforcing member 3, and the built-in device 1 is fixed in the reinforcing member 3 by the attaching tool 4 and installed in the casing 2. A first shock absorbing member 9 is disposed in a first space s1 between the built-in device 1 and the reinforcing member 3, and a second shock absorbing member 10 is disposed in the second space s2 between the reinforcing member 3 and the bottom of the casing 2.