A surgical instrument device includes a surgical instrument portion which is used in a surgical operation, a slave arm which holds the surgical instrument, a driving rod which is formed in a shaft shape, of which one end portion in the axial direction is connected to the surgical instrument and the other end portion in the axial direction is supported by the slave arm, and which transmits a force between the surgical instrument and the slave arm, a distance change detecting unit which detects a change in distance between two points in the axial direction of the driving rod based on a distance when no load is applied to the surgical instrument, and a force calculating unit which calculates a force applied from the surgical instrument or the slave arm to the driving rod based on the change in distance detected by the distance change detecting unit.
