A sleepiness estimating device (1) includes an environmental information detector (150) that detects a plurality of conditions of an environment surrounding a user (U) and outputs environmental information indicating the detected conditions of the environment, a calculator (2) that calculates an environmental level indicating a degree of how likely the user (U) becomes sleepy in the environment in accordance with the environmental information output by the environmental information detector (150), and an output (130) that outputs the environmental level calculated by the calculator (2).