A toothbrush attachment comprising: a toothbrush module including: a sensor unit that detects a predetermined physical quantity concerning a toothbrush having a substantially rod-like handle with a first end at which bristle tufts are implanted; and a wireless transmission unit that transmits a radio signal indicating the physical quantity detected by the sensor unit; a housing unit that houses the sensor unit and the wireless transmission unit and has a substantially flat bottom surface, an upper surface opposite to the bottom surface, and a side surface connecting the bottom surface and the upper surface to each other; an instruction reception unit disposed on the upper surface for receiving a pressing force as a start instruction for starting an operation of the toothbrush module; a coupling mechanism including a holding unit and a recess, the holding unit and the recess being constituted with the coupling mechanism by an elastomer, the holding unit having an insertion hole whose depth direction extends along an axial direction of the handle so that the insertion hole receives a second end of the handle, the insertion hole having a bottom part covering the insertion hole and facing the instruction reception unit, wherein the recess receives and holds the housing unit so that the housing unit covers the upper surface and the side surface, wherein the holding unit removably couples the second end of the handle and the housing by elastically holding the handle at an upper surface side of the housing with an elastic force of the elastomer so that the axial direction of the handle is substantially perpendicular to the bottom surface, thereby allowing the toothbrush to stand by itself with the bottom surface facing downward, and the second end of the handle to face the instruction reception unit, and wherein the instruction reception unit receives a pressing force as the start instruction when the bottom is pushed by the second end of the handle. a sensor unit that detects a predetermined physical quantity concerning a toothbrush having a substantially rod-like handle with a first end at which bristle tufts are implanted; and a wireless transmission unit that transmits a radio signal indicating the physical quantity detected by the sensor unit; a housing unit that houses the sensor unit and the wireless transmission unit and has a substantially flat bottom surface, an upper surface opposite to the bottom surface, and a side surface connecting the bottom surface and the upper surface to each other; an instruction reception unit disposed on the upper surface for receiving a pressing force as a start instruction for starting an operation of the toothbrush module; a coupling mechanism including a holding unit and a recess, the holding unit and the recess being constituted with the coupling mechanism by an elastomer, the holding unit having an insertion hole whose depth direction extends along an axial direction of the handle so that the insertion hole receives a second end of the handle, the insertion hole having a bottom part covering the insertion hole and facing the instruction reception unit, wherein the recess receives and holds the housing unit so that the housing unit covers the upper surface and the side surface, wherein the holding unit removably couples the second end of the handle and the housing by elastically holding the handle at an upper surface side of the housing with an elastic force of the elastomer so that the axial direction of the handle is substantially perpendicular to the bottom surface, thereby allowing the toothbrush to stand by itself with the bottom surface facing downward, and the second end of the handle to face the instruction reception unit, and wherein the instruction reception unit receives a pressing force as the start instruction when the bottom is pushed by the second end of the handle.