An exhaust gas purification device includes: an actual pressure difference obtainer that acquires an actual pressure difference which is an actual measurement value of a pressure difference of a filter; a flow rate obtainer that acquires a flow rate of exhaust gas flowing into the filter; a calculation pressure difference calculator that calculates a calculation pressure difference which is a calculated value of the pressure difference of the filter in a normal state when the exhaust gas flows into the filter with the flow rate acquired by the flow rate obtainer; and an abnormality determiner that performs an abnormality determination of the filter based on a pressure difference variation ratio which is a ratio between a variation in the actual pressure difference and a variation in the calculation pressure difference in response to a variation in the flow rate of the exhaust gas.