A medium storage box for mounting on a financial device for performing medium processing, comprising: a cassette body having a storage space in which a medium is stored; a cassette door coupled to the cassette body to open or close the storage space; a door opening detection unit that is configured to generate an open detection signal when the cassette door is opened; a microcomputer configured to determine that the cassette door is opened when the open detection signal is received by the microcomputer, and for storing the determined opening information of the cassette door in a cassette memory; and a battery that is configured to supply power to the door opening detection unit and the microcomputer, characterized in that the medium storage box further comprises a transistor disposed between the door opening detection unit and the battery, and being turned on by receiving the open detection signal of the door opening detection unit, wherein the transistor includes a collector terminal, a base terminal, and an emitter terminal; an input terminal of the battery is connected to the collector terminal of the transistor; the door opening detection unit is connected to the base terminal of the transistor; and a low voltage line is connected to the emitter terminal of the transistor, the transistor configured to amplify an input signal from the door opening detection unit and transmit the amplified signal to the collector terminal, wherein when the door opening detection unit generates the open detection signal, the transistor is turned on and then the power of the battery is supplied to the microcomputer, wherein when the power of the battery is supplied to the microcomputer, the microcomputer is configured to recognize that the cassette door is opened. a cassette body having a storage space in which a medium is stored; a cassette door coupled to the cassette body to open or close the storage space; a door opening detection unit that is configured to generate an open detection signal when the cassette door is opened; a microcomputer configured to determine that the cassette door is opened when the open detection signal is received by the microcomputer, and for storing the determined opening information of the cassette door in a cassette memory; and a battery that is configured to supply power to the door opening detection unit and the microcomputer, characterized in that the medium storage box further comprises a transistor disposed between the door opening detection unit and the battery, and being turned on by receiving the open detection signal of the door opening detection unit, wherein the transistor includes a collector terminal, a base terminal, and an emitter terminal; an input terminal of the battery is connected to the collector terminal of the transistor; the door opening detection unit is connected to the base terminal of the transistor; and a low voltage line is connected to the emitter terminal of the transistor, the transistor configured to amplify an input signal from the door opening detection unit and transmit the amplified signal to the collector terminal, wherein when the door opening detection unit generates the open detection signal, the transistor is turned on and then the power of the battery is supplied to the microcomputer, wherein when the power of the battery is supplied to the microcomputer, the microcomputer is configured to recognize that the cassette door is opened.