A driving unit for use in an electric assist bicycle, comprising: a housing a crankshaft positioned to extend through the housing; a motor located within the housing; and a transmission shaft located within the housing and extending parallel to a central axis of the crankshaft the motor including: a rotor; an output shaft configured to rotate together with the rotor and extending parallel to the central axis of the crankshaft; and an output gear located on the output shaft, the driving unit further comprising: a first transmission gear located on the transmission shaft and configured to engage the output gear, the first transmission gear including more cogs than the output gear does; a second transmission gear located on the transmission shaft; and a driven gear positioned within the housing, located on the crankshaft and configured to engage the second transmission gear, the driven gear including more cogs than the second transmission gear does, wherein, if out of the motor, first transmission gear and driven gear, a first component is a component with the largest diameter as viewed in an axial direction of the crankshaft, a second component is a component with the second largest diameter, and a third component is a component with the smallest diameter, one of the first and second components is the driven gear, as viewed in an axial direction of the crankshaft, at least part of the first component overlaps the second component, at least part of the third component overlaps an area where the first and second components (104,30) overlap, a first line segment connecting a rotational center of the first component with a rotational center of the second component, a second line segment connecting the rotational center of the second component with a rotational center of the third component, and a third line segment connecting the rotational center of the third component with the rotational center of the first component form a triangle, and the first line segment is longer than the second line segment and longer than the third line segment, characterized by the second transmission gear being positioned within the housing. a housing a crankshaft positioned to extend through the housing; a motor located within the housing; and a transmission shaft located within the housing and extending parallel to a central axis of the crankshaft the motor including: a rotor; an output shaft configured to rotate together with the rotor and extending parallel to the central axis of the crankshaft; and an output gear located on the output shaft, a rotor; an output shaft configured to rotate together with the rotor and extending parallel to the central axis of the crankshaft; and an output gear located on the output shaft, the driving unit further comprising: a first transmission gear located on the transmission shaft and configured to engage the output gear, the first transmission gear including more cogs than the output gear does; a second transmission gear located on the transmission shaft; and a driven gear positioned within the housing, located on the crankshaft and configured to engage the second transmission gear, the driven gear including more cogs than the second transmission gear does, wherein, if out of the motor, first transmission gear and driven gear, a first component is a component with the largest diameter as viewed in an axial direction of the crankshaft, a second component is a component with the second largest diameter, and a third component is a component with the smallest diameter, a first transmission gear located on the transmission shaft and configured to engage the output gear, the first transmission gear including more cogs than the output gear does; a second transmission gear located on the transmission shaft; and a driven gear positioned within the housing, located on the crankshaft and configured to engage the second transmission gear, the driven gear including more cogs than the second transmission gear does, wherein, if out of the motor, first transmission gear and driven gear, a first component is a component with the largest diameter as viewed in an axial direction of the crankshaft, a second component is a component with the second largest diameter, and a third component is a component with the smallest diameter, one of the first and second components is the driven gear, as viewed in an axial direction of the crankshaft, at least part of the first component overlaps the second component, at least part of the third component overlaps an area where the first and second components (104,30) overlap, a first line segment connecting a rotational center of the first component with a rotational center of the second component, a second line segment connecting the rotational center of the second component with a rotational center of the third component, and a third line segment connecting the rotational center of the third component with the rotational center of the first component form a triangle, and the first line segment is longer than the second line segment and longer than the third line segment, characterized by the second transmission gear being positioned within the housing.