apparatus for inserting elastic strips into elastic leg diapers wherein elastic strips are adhesively secured continuously along the crotch area and in relaxed condition along the waist areas including a mechanism for feeding a continuous strip of elastic at a constant rate , a mechanism for feeding a continuous sheet of diaper material at a constant rate , and an oscillating arm for guiding the sheet of diaper material and inducing periodic variations in the velocity or distance of the diaper material with respect to the elastic feeding mechanism , thereby alternately stretching and relaxing predetermined lengths of continuous elastic strips as they are adhesively secured to the diaper material .