To prevent the deflection angle of a needle from following a disturbance such as noise by calculating the difference between the present deflection angle and the previous deflection angle as a change quantity, and adjusting the change quantity within the update angle range of the needle in a needle instrument and its needle adjusting method.

A deflection angle determining means 210 repeatedly determines the deflection angle of a needle deflected by the drive of a driving means according to the input quantity, a change quantity calculating means 220 calculates a change quantity, and a change quantity adjusting means 230 adjusts the change quantity within the update angle range of the needle. An update angle determining means 260 determines the update deflection angle of the needle according to the adjusted change quantity of the previous deflection angle by a change quantity adjusting means. An update angle range determination variable setting means 270 corrects the determined update deflection angle to suppress the effect of a disturbance and sets update angle range determination variables.