A plasticizing device includes a material reservoir which has an input port and is configured to retain a material, a plasticizer which has a screw and a case housing the screw and provided with a feed port communicated with the input port, and which is configured to plasticize the material to generate a plasticized material, a coupling pipe having a coupling path configured to connect the input port and the feed port to each other, a material sensor which has a light emitter configured to emit light toward the screw via the feed port, and a light receiver configured to receive reflected light of the light, and which is configured to detect a remaining amount of the material, and a controller configured to control the material reservoir, wherein the material reservoir has a material feed mechanism configured to feed the material to the coupling path, and the controller controls the material feed mechanism to feed the material to the coupling path when the remaining amount of the material detected by the material sensor is smaller than a reference value.