A fuel property detecting device includes an electrode part; a voltage conversion part; a standard voltage application part; an amplifying part; a temperature detection unit; a storage unit; a first calculation unit; a second calculation unit for calculating alcohol concentration in fuel based on capacitance calculated by the first unit, present fuel temperature, and a map indicating a first relationship between capacitance and fuel temperature; a third calculation unit; a conductivity determination unit for determining whether present conductivity calculated by the third unit is a predetermined conductivity or larger; a fourth calculation unit for calculating a second relationship between conductivity and fuel temperature based on past conductivity, past fuel temperature, present conductivity calculated by the third unit, and present fuel temperature; and an abnormality determination unit for determining whether the electrode part is abnormal based on the second relationship, and a coefficient of temperature properties indicating the second relationship.