To provide a sensor apparatus and sensor system using a low-power input source such as a microbial fuel cell, provided is a sensor apparatus including a microbial fuel cell; a boosting DC-DC circuit that operates based on an input voltage from the microbial fuel cell and boosts the input voltage; a power storage element that stores power output from the boosting DC-DC circuit; and a sensor element that operates based on power output from the power storage element, as well as a sensor system that includes this sensor apparatus and a wireless communication apparatus.