A joint for connecting a motor unit to a power cord of a dental handpiece, comprising: a generally cylindrical motor casing, a motor unit detachably accommodated in said motor casing and supplying driving force to a dental tool, a generally cylindrical end cap connected to a hose which accommodates a power cord for supplying power to the motor unit, and detachably connectable to one end of the motor casing, and a motor-unit-side connector and a power-cord-side connector arranged between the motor casing and the end cap for mutual electrical engagement, said motor casing having an opening at its end to be connected to said end cap, said end cap having a distal end of a larger outer diameter which is the same as the outer diameter of the proximal end of the motor casing and a proximal end of a smaller outer and inner diameter, with a contour tapered from the distal to proximal end, said end cap having an opening at its end to be connected to said motor casing, connection of the motor casing to the end cap causing said motor-unit-side connector and thus said motor unit to be electrically connected to said power-cord-side connector and thus the power cord, wherein said motor-unit-side connector is arranged projecting outwards from the opening of the motor casing, and said power-cord-side connector is arranged offset from the opening of said end cap into an interior of the end cap, and wherein said motor-unit-side connector is connectable to saidpower-cord-side connector inside the end cap, wherein said joint further comprises a step protruding from the opening of the motor casing, and having a smaller diameter sized so that said opening of the end cap is capable of fitting thereon, wherein said step of the motor casing has a male thread formed on its outer circumference, and said end cap has a female thread formed circumferentially on its inner surface near the opening, so that the motor casing is capable of being screwed and fixed to the end cap, and characterized in that said power-cord-side connector is arranged inside the end cap in a proximal end portion of a smaller diameter than the distal end, and said motor-unit-side connector, when connected to the power-cord-side connector, is arranged in said proximal end portion of the end cap. a generally cylindrical motor casing, a motor unit detachably accommodated in said motor casing and supplying driving force to a dental tool, a generally cylindrical end cap connected to a hose which accommodates a power cord for supplying power to the motor unit, and detachably connectable to one end of the motor casing, and a motor-unit-side connector and a power-cord-side connector arranged between the motor casing and the end cap for mutual electrical engagement, said motor casing having an opening at its end to be connected to said end cap, said end cap having a distal end of a larger outer diameter which is the same as the outer diameter of the proximal end of the motor casing and a proximal end of a smaller outer and inner diameter, with a contour tapered from the distal to proximal end, said end cap having an opening at its end to be connected to said motor casing, connection of the motor casing to the end cap causing said motor-unit-side connector and thus said motor unit to be electrically connected to said power-cord-side connector and thus the power cord, wherein said motor-unit-side connector is arranged projecting outwards from the opening of the motor casing, and said power-cord-side connector is arranged offset from the opening of said end cap into an interior of the end cap, and wherein said motor-unit-side connector is connectable to saidpower-cord-side connector inside the end cap, wherein said joint further comprises a step protruding from the opening of the motor casing, and having a smaller diameter sized so that said opening of the end cap is capable of fitting thereon, wherein said step of the motor casing has a male thread formed on its outer circumference, and said end cap has a female thread formed circumferentially on its inner surface near the opening, so that the motor casing is capable of being screwed and fixed to the end cap, and characterized in that said power-cord-side connector is arranged inside the end cap in a proximal end portion of a smaller diameter than the distal end, and said motor-unit-side connector, when connected to the power-cord-side connector, is arranged in said proximal end portion of the end cap.