An operation unit is used for a user to perform a tilt operation. The operation unit includes a disc-shaped detection subject member with a detection subject plane, which intersects with a basic axis Q of the operation unit and is movable integrally with the operation unit. Three detecting units are fixed in three different disposed positions surrounding a neutral axis N to detect displacement parallel with the neutral axis, which is generated by movement of the detection subject plane. A computing unit determines three-dimensional detected positions M1, M2, M3 of the detection subject plane by using (i) the disposed positions (X, Y) of the three detecting units and (ii) displacement detection outputs Z detected by the three detecting units. A tilt direction, in which the operation unit is tilted, is determined using a displacement plane DP defined by the three-dimensional detected positions M1, M2, M3.