A rotational driving force imparting device includes an electric motor device (50) and a planetary gear transmission device (10). Among a sun gear shaft (12) of a planetary gear transmission device (10), a planetary gear carrier shaft (27), and an internal gear carrier shaft (37), one shaft forms an output shaft (Ao), another shaft forms a constant speed input shaft (Ac), and the other shaft forms a variable speed input shaft (Av). The electric motor device (50) includes a constant speed motor (51) including a constant speed rotor (52) that rotates about a shaft line (Ar) and is connected to a constant speed input shaft (Ac), and a variable speed motor (71) including a variable speed rotor (72) that rotates about the shaft line (Ar) and is connected to a variable speed input shaft (Av). A shaft insertion hole (74) forming a cylindrical shape about the shaft line (Ar) and penetrating in the axial direction is formed in the variable speed rotor (72), and the constant speed rotor (52) is inserted into the shaft insertion hole (74).