A pulse detection method resistant to changes in an imaging environment is provided.A biological information detection device includes an imaging unit that images reflected light from a target object and outputs a video signal including a plurality of wavelength components, a reflected light analysis unit that obtains a wavelength and an intensity of the reflected light from the video signal, a wavelength fluctuation detection unit that detects difference between the wavelength of the reflected light of each time and the wavelength of the reflected light of a time before each of the time, and a pulse detecting unit that detects a change in accordance with a time of the detected difference as a pulse.