Physical level-based security system for data security of security terminal and method using the same

A physical level-based security method for data security of a security terminal, comprising:

• individually connecting at least one normal terminal corresponding to an external network and a security terminal corresponding to an internal network to an interface device;
• selecting any one input target terminal to which input information of a user is to be transmitted, from among the at least one normal terminal and the security terminal;
• transmitting the input information to the input target terminal based on the interface device;
• and
• relaying, by the interface device, data from the at least one normal terminal to the security terminal in conformity with unidirectional transmission, wherein the interface device relays the data such that a communication event of the security terminal, corresponding to at least one of a control signal, a data signal, and a timing and signal waveform, does not influence a communication event of the at least one normal terminal, corresponding to at least one of a control signal, a data signal, and a timing and signal waveform.