A tire pressure monitoring apparatus includes a frequency detection unit configured to detect a resonant frequency according to a tire pressure; a calculation unit configured to accumulate the resonant frequency and calculate an average frequency and a frequency variance; a coordinate system setting unit configured to locate a first average variance point corresponding to the average frequency and the frequency variance, on an average-variance plane, and locate second average variance points corresponding to average frequencies and frequency variances of resonant frequencies measured for types of tires, on the average-variance plane; a tire determination unit configured to determine a type of a tire in consideration of distances between the first and second average variance points; and a low-pressure frequency setting unit configured to set a low-pressure frequency according to the determined type of the tire, as a reference low-pressure frequency for determining whether the tire pressure is a low pressure.