Since the sleepiness degree is changed by a daytime activity, a time and a sleep state, a sleepiness prediction apparatus in view of these is provided. The sleepiness prediction apparatus 10 includes a sensor head 14 mounted on a fingertip, and a main body 12 of a wrist watch type, measures a sleep state relevant value relevant to a sleep state of a test subject, measures a daytime activity relevant value relevant to a daytime activity of the test subject, calculates, based on the sleep state relevant value and the daytime activity relevant value, an accumulated sleepiness degree predicted to be accumulated by a sleep history of the test subject and a daytime activity, calculates a biological rhythm sleepiness degree based on a biological rhythm changing according to a time, and calculates a comprehensive sleepiness degree corresponding to a time based on the accumulated sleepiness degree and the biological rhythm sleepiness degree.