To measure the contact force between a pantograph and contact wire the author is proposing to use a new inversion method, the distinct feature of which is to reduce restraints on the sensor arrangement to facilitate contact force measurement. The contact force is calculated using the convolution between the sensor output and impulse response function, which is defined as the relationship between the former and the contact force. To achieve sufficient levels of precision, high order vibration modes of the panhead have to be taken into consideration by applying a pseudo-inverse matrix. The author has confirmed the accuracy of this method by numerical calculations and an excitation test on a currently-used pantograph.