A controller for a steering device (2; 200) includes an electronic control unit (1) configured to control the steering device (2). The electronic control unit (1) is configured to acquire an action force and to calculate a basic reaction force based on the acquired action force. The action force includes at least two of axial forces of a plurality of types and a tire force. The axial forces of a plurality of types are applied to a turning shaft that is connected to turning wheels (4). The tire force is applied to the turning wheels (4). The electronic control unit (1) is configured to, when one predetermined force of the acquired action force is abnormal, calculate the basic reaction force such that a contribution proportion of the predetermined force to the basic reaction force is lower than a contribution proportion when the predetermined force is not abnormal.