Abstract: An investing method, a device for investing, and a system for investing which do not expose a client's invested capital to risks such as loss of principal value, for example, and yet which are capable of producing large profits and are attractive to both the client and a financial institution. Disclosed is an investing method in which a part or all of interest applied by the financial institution to the investment principal invested by the client is used as funds for investing and is appropriated for purchases of options based on predictions by the client regarding predetermined phenomena on each of the predetermined dates, and these option purchases are repeated during a given period having been determined in advance.