An abnormality detection method for a vehicle body tilt control device provided on a vehicle having a vehicle body, a pair of bogies located toward a front and a rear of the vehicle body and a pair of air springs located to a left and right of each bogie and supporting the vehicle body, the vehicle body tilt control device controlling supply/exhaust to/from the air springs to tilt the vehicle body, the abnormality detection method comprising the steps of: preparing a state estimation model for each of the bogies; and using the state estimation model to detect which one of the air springs has an air supply/exhaust abnormality, wherein the state estimation model is a mathematical model that, when a first flow rate command value indicating a flow rate of air supplied to/exhausted from one air spring is input, multiplies the first flow rate command value by a first virtual gain that is a state variable, when a second flow rate command value indicating a flow rate of air supplied to/exhausted from the other air spring is input, multiplies the second flow rate command value by a second virtual gain that is a state variable, and outputs an average of heights of the air springs based on an average of the first flow rate command value multiplied by the first virtual gain and the second flow rate command value multiplied by the second virtual gain, wherein the step of detecting an abnormality includes the steps of: estimating a value of the first virtual gain and a value of the second virtual gain by using, as a value output by the state estimation model, an average of a value obtained by observing a height of the one air spring when supply/exhaust is controlled based on the first flow rate command value and a value obtained by observing a height of the other air spring when supply/exhaust is controlled based on the second flow rate command value; and determining that there is an abnormality in the supply/exhaust for the one air spring when the estimated value of the first virtual gain is below a predetermined threshold and determining that there is an abnormality in the supply/exhaust for the other air spring when the estimated value of the second virtual gain is below the predetermined threshold. preparing a state estimation model for each of the bogies; and using the state estimation model to detect which one of the air springs has an air supply/exhaust abnormality, wherein the state estimation model is a mathematical model that, when a first flow rate command value indicating a flow rate of air supplied to/exhausted from one air spring is input, multiplies the first flow rate command value by a first virtual gain that is a state variable, when a second flow rate command value indicating a flow rate of air supplied to/exhausted from the other air spring is input, multiplies the second flow rate command value by a second virtual gain that is a state variable, and outputs an average of heights of the air springs based on an average of the first flow rate command value multiplied by the first virtual gain and the second flow rate command value multiplied by the second virtual gain, wherein the step of detecting an abnormality includes the steps of: estimating a value of the first virtual gain and a value of the second virtual gain by using, as a value output by the state estimation model, an average of a value obtained by observing a height of the one air spring when supply/exhaust is controlled based on the first flow rate command value and a value obtained by observing a height of the other air spring when supply/exhaust is controlled based on the second flow rate command value; and determining that there is an abnormality in the supply/exhaust for the one air spring when the estimated value of the first virtual gain is below a predetermined threshold and determining that there is an abnormality in the supply/exhaust for the other air spring when the estimated value of the second virtual gain is below the predetermined threshold. estimating a value of the first virtual gain and a value of the second virtual gain by using, as a value output by the state estimation model, an average of a value obtained by observing a height of the one air spring when supply/exhaust is controlled based on the first flow rate command value and a value obtained by observing a height of the other air spring when supply/exhaust is controlled based on the second flow rate command value; and determining that there is an abnormality in the supply/exhaust for the one air spring when the estimated value of the first virtual gain is below a predetermined threshold and determining that there is an abnormality in the supply/exhaust for the other air spring when the estimated value of the second virtual gain is below the predetermined threshold.