Input device and method for controlling input device

An input device includes a first part and a second part configured to move relative to each other according to an input operation, a magnetic viscous fluid whose viscosity changes according to a magnetic field, and a magnetic-field generator that generates the magnetic field applied to the magnetic viscous fluid. The second part includes a first surface and a second surface that are arranged in a direction orthogonal to a direction of relative movement between the first part and the second part. Gaps are formed between the first surface and the first part and between the second surface and the first part, and the magnetic viscous fluid is present in at least a part of the gaps.