An alpha ray observation device and an alpha ray observation method are provided that can correctly evaluate a signal derived from alpha rays. The alpha ray observation device according to an embodiment includes a device housing 10, an incident window 2, a condenser 3, an optical path changer 4, and a first optical detector 5. The device housing 10 is provided with an opening. The incident window 2 is provided at the opening, and can block beta rays. Emitted light originated by alpha rays caused from the measurement object set outside of the device housing 10 enters the inside of the device housing 10 through the incident window 2 with beta rays being blocked, and is condensed by the condenser 3, and the optical path is changed by the optical path changer 4, and subsequently the light is detected by the first optical detector 5. The first optical detector 5 outputs a signal according to the amount of detected light.