An inspection system, comprising: a data acquisition means arranged to acquire measured data being time-series data of measured values to be measured by causing a railway vehicle including a vehicle body, a bogie (12a, 12b), and a wheel set (13a to 13b) to travel on a track; a frequency adjustment means arranged to reduce a signal strength of a low-frequency component to be generated due to the railway vehicle traveling on a curved portion of the track of the time-series data of a measured value of the measured data of a forward-and-backward-direction force varying in a value according to a state of the railway vehicle or of the time-series data of estimated values of a physical quantity varying in a value according to a state of the railway vehicle; and a track state calculation means arranged to derive information reflecting a state of the track, wherein the measured data contain a measured value of the forward-and-backward-direction force, the low-frequency component is a signal contained in the time-series data of a measured value of the measured data, the low frequency component not being measured when the railway vehicle is traveling on a linear portion of the track, but is measured when the railway vehicle is traveling on a curved portion of the track, the forward-and-backward-direction force is a force in a forward and backward direction to occur in a member disposed between the wheel set (13a to 13b) and the bogie (12a, 12b) on which the wheel set (13a to 13b) is provided, the member is a member for supporting an axle box, the forward and backward direction is a direction along a traveling direction of the railway vehicle, the frequency adjustment means includes a first frequency adjustment means arranged to reduce the signal strength of the low-frequency component to be generated due to the railway vehicle traveling on a curved portion of the track from the time-series data of the measured value of the forward-and-backward-direction force, the track state calculation means is arranged to use a relational expression representing the relation between information reflecting a state of the track at a position of the wheel set (13a to 13b) and the forward-and-backward-direction force and a value of the forward-and-backward-direction force from which the signal strength of the low-frequency component has been reduced by the first frequency adjustment means to derive information reflecting a state of the track, and the relational expression is an expression not including a curvature radius of a rail. a data acquisition means arranged to acquire measured data being time-series data of measured values to be measured by causing a railway vehicle including a vehicle body, a bogie (12a, 12b), and a wheel set (13a to 13b) to travel on a track; a frequency adjustment means arranged to reduce a signal strength of a low-frequency component to be generated due to the railway vehicle traveling on a curved portion of the track of the time-series data of a measured value of the measured data of a forward-and-backward-direction force varying in a value according to a state of the railway vehicle or of the time-series data of estimated values of a physical quantity varying in a value according to a state of the railway vehicle; and a track state calculation means arranged to derive information reflecting a state of the track, wherein the measured data contain a measured value of the forward-and-backward-direction force, the low-frequency component is a signal contained in the time-series data of a measured value of the measured data, the low frequency component not being measured when the railway vehicle is traveling on a linear portion of the track, but is measured when the railway vehicle is traveling on a curved portion of the track, the forward-and-backward-direction force is a force in a forward and backward direction to occur in a member disposed between the wheel set (13a to 13b) and the bogie (12a, 12b) on which the wheel set (13a to 13b) is provided, the member is a member for supporting an axle box, the forward and backward direction is a direction along a traveling direction of the railway vehicle, the frequency adjustment means includes a first frequency adjustment means arranged to reduce the signal strength of the low-frequency component to be generated due to the railway vehicle traveling on a curved portion of the track from the time-series data of the measured value of the forward-and-backward-direction force, the track state calculation means is arranged to use a relational expression representing the relation between information reflecting a state of the track at a position of the wheel set (13a to 13b) and the forward-and-backward-direction force and a value of the forward-and-backward-direction force from which the signal strength of the low-frequency component has been reduced by the first frequency adjustment means to derive information reflecting a state of the track, and the relational expression is an expression not including a curvature radius of a rail.