A reciprocating rocking device for the rocking of a chair or cradle, the chair or cradle having rockers and a seat member, the reciprocating rocking device comprising a base secured to the rockers, the base comprising a first bracket, a second bracket secured to the seat member of the chair or cradle, a tension member connected to the second bracket, an eccentric, the eccentric constantly engaged with the second bracket and, a motor secured to the first bracket, the motor having a drive shaft operatively arranged to drive the eccentric, wherein the motor is coaxially arranged with the eccentric.