A biological information detection device or the like which can determine a mounted state or an unmounted state with high accuracy, or can appropriately present information on the basis of a determination result is to be provided.A biological information detection device includes a pulse wave detection unit 10 that outputs a pulse wave sensor signal and a processing unit 100 that processes the pulse wave sensor signal, in which the processing unit 100 performs a detachment detection process of the biological information detection device on the basis of a DC component change value of the pulse wave sensor signal in a predetermined period.