A system for providing a home health care service includes a health care center, a service recipient device, and the Internet that connects these components. The health care center: is constructed on the Internet; includes a database for registering personal data that are necessary for the health care of registered at-home patients as basic health care data and storing measurement data that are provided from at-home patients over the course of time; and has the functions of inferring the health conditions of at-home patients based on the measurement data and the basic health care data, and offering appropriate services necessary for inferred health conditions. The service recipient device includes a biosensor and a signal processor. The biosensor detects chemical components contained in a substance that is discharged from the human body and converts detected values to electrical signals at the point of discharge.