This study aimed to explore the relationship between comfortable diaper placement and the movements of the nurse during this activity. We assessed the flexion and extension of the nurses’ left and right elbow joints during diaper placement using a three-dimensional motion-tracking device and network cameras while the nurses placed a diaper and pad on a manikin representing an elderly female. The patient’s comfort level while wearing the diaper was assessed by how quickly the simulated urine was absorbed, whether the urine remained absorbed, whether residual urine pooled in the vulva, and whether the diaper was in sufficient contact with the pressure-sensor sheet. The participants were 17 female nurses, and 170 motions were analyzed. The relationship between the comfort indicators and diaper-placement motions including activities such as molding the pad into a cone before applying it（odds ratio, 7.87, 95% confidence interval, 2.29-27.01）, fitting the three-dimensional gathers of the diaper to the groin area for a secure fit（5.17, 1.65-16.15）, and placing a finger in the groin region after placement to check that the diaper was secure（0.27, 0.09-0.77）, was statistically analyzed. Optimal placement of the diaper in the groin area required flexing and extending the elbow joint on average 13 times for the left arm and 12 times for the right arm using a wiggling movement.