Disappearance process of diurnal naps of infants until ３ years after birth.

The study aimed at describing the developmental change of diurnal naps during 2 to 46 months of age, with the data of sleep diary recorded by nursery teachers at a nursery school. Diurnal naps in the morning almost disappeared at 12 months after birth and completely disappeared by 18 months, while daytime nap in the afternoon peaked quantitatively at 18 months and then gradually decreased. The pattern of decrease of afternoon naps consisted from disappearance of nap outside of the narrower time zone （13:00 to 15:01） and concentration of nap in this time zone.