A control device for a work machine is a device for controlling a working unit of a work machine to excavate an object to be excavated. The control device includes a control unit for controlling the working unit to prevent a working implement of the working unit from crossing a predetermined target profile, and a switching unit for defining the target profile as an offset profile separated by a predetermined distance from a target excavation profile that is a target profile for finishing of the object to be excavated or the target excavation profile, based on an attitude of the working implement relative to the target excavation profile.