Disclosed is a speed reducer group comprising: a first speed reducer having a first crank assembly which swings a first swing gear to generate a relative rotation between a first outer cylindrical portion and a first carrier portion around a first spindle defined as a relative rotary shaft between the first outer cylindrical portion and the first carrier portion by performing a rotary motion around a first transmission shaft spaced apart from the first spindle by a first distance; and a second speed reducer having a second crank assembly which swings a second swing gear to generate a relative rotation between a second outer cylindrical portion and a second carrier portion around a second spindle defined as a relative rotary shaft between the second outer cylindrical portion and the second carrier portion by performing a rotary motion around a second transmission shaft spaced apart from the second spindle by a second distance different from the first distance. The speed reducer group of the present invention can reduce labor for designing a new speed reducer.