Many researchers have been trying to harvest electric energy from structural vibration for various self-powered small systems. To enhance the harvesting performance self-powered switched shunt circuits have been invented. However, all of these studies have been limited to the energy harvesting form sinusoidal vibrations of a single-degree-of-frcedom (SDOF) structure. In our study, a multiple-degree-of-freedom (MDOF) structure is randomly excited. By using a piezoelectric transducer and a rectifier, electrical energy is taken out from the randomly vibrating structure and stored in a capacitor connected to an electric load. In various conditions, we study how much electrical energy can be stored with and without our switched shunt circuit. Our switched shunt circuit is composed of inductors, resistors, capacitors, diodes, thyristors, and programmable unijunction transistors (PUT), which was originally invented for semi-active vibration suppression. Experimental results show that the stored electrical energy can be increased more than twice with our simple shunt circuit even when the structure is randomly vibrating.