A method of detecting an abnormal electric current in a vehicle to detect passage of an abnormal electric current through an electric wire for establishing the connection between a load to which electric power is supplied and a power source, the method of detecting an abnormal electric current in a vehicle comprising the steps of: (a) detecting values of electric currents which pass through the electric wire at predetermined sampling intervals; (b) counting the number of times in a unit detection period that a sampled electric current having a value larger than a predetermined value is detected and determining passage of an abnormal electric current through the electric wire when the number of counts is larger than a first number of times; and (c) counting the number of times that a sampled electric current having a value larger than the predetermined value is detected in a unit detection period after the unit detection period in terms of time in a case where the number of counts is smaller than the first number of times and except for zero and determining passage of an abnormal electric current through the electric wire when the number of counts is larger than a second number of times.