Disclosed is an apparatus for regulating viscosity of ink, which is installed on a flow path of ink in a printing device for regulation of ink viscosity. The apparatus includes a housing installed on the flow path and having an introduction hole and a discharge hole through which ink is introduced and discharged; a rotary shaft installed in the housing and to which at least one rotating fan is coupled to rotate along with flow of the ink; a sensed member having a sensed body at one end thereof and coupled to the rotary shaft to rotate together with the rotary shaft; and a sensor for sensing the sensed body.