Planetary gear assembly, power-split stepless transmission, and transmission structure

[Problem] To provide a planetary gear assembly that, while increasing the speed change range of a power-split stepless transmission formed in cooperation a stepless transmission, can reduce the overall size of the power-split stepless transmission. [Solution] The planetary gear assembly according to the present invention includes: a cylindrical transmission shaft, an output shaft inserted into the transmission shaft, first and second planetary gear mechanisms each having a first sun gear supported to the transmission shaft without a relative rotation about an axial line, first and second clutch mechanisms that are placed coaxially with the transmission shaft, and that engage and disengage a power transmission of power to standard rotary speed power input units of the first and second planetary gear mechanisms, and a connection member extrapolated to the transmission shaft with a free relative rotation about an axial line. The connection member, without a relative rotation around an axial line, connects, within the first planetary gear mechanism, a planetary element that is other than a sun gear and a planetary element that forms a standard rotary speed power input unit, with, within the second planetary gear mechanism, a planetary element that is other than a sun gear and a planetary element that forms a standard rotary speed power input unit, and the connection member, meanwhile, is non-rotatable relative to the output shaft about an axial line.