A valve control device includes a valve unit disposed in a cooling water circuit, and a control part which controls operation of the valve unit. The control part has a rotation angle instruction part, a duty ratio calculator and a determiner. The rotation angle instruction part calculates an instruction value of a rotation angle in response to an operational status of an internal-combustion engine. The duty ratio calculator calculates a duty ratio representing a ratio of ON period to OFF period regarding a voltage applied to an electric motor based on a difference between a detection value of the rotation angle detected by a detector and the instruction value of the rotation angle, and regulates the duty ratio to be lower than or equal to a predetermined upper limit. The determiner determines whether the duty ratio continues to be the upper limit during a predetermined period.