There is provided an electrical device's casing capable of reducing vibration generated by the electrical device while the device is operating. A converter case (10) encasing a reactor which generates vibration while operating includes: a plate-shaped base (12) having a front surface and a rear surface, the reactor being to be mounted on the front surface; a reactor case (30) erected from the front surface of the base (12) and surrounding an outer periphery of the reactor; a reinforcing portion (40) provided outside the reactor case (30) and configured to increase stiffness of the base (12); and a rib (50) coupling the reactor case (30) and the reinforcing portion (40) to each other.