A biological signal detecting section (41) is provided that detects a biological information signal (S2) (such as a heartbeat signal) having an amplitude that changes in accordance with the biological activity of a person going to bed. Also, a body movement signal detecting section (20, 33) is provided that detects a body movement signal (S1) having an amplitude that changes in accordance with the magnitude of the body movement of said person. Also, a determination section (44) is provided that determines that the person has gotten into bed if a first bed-entrance determination condition and/or a second bed-entrance determination condition are/is satisfied, the first bed-entrance determination condition being a condition according to which it is determined that the person has gotten into bed if the amplitude of the body movement signal (S1) continues to exceed a body movement threshold (V1) for at least a bed-entrance body-movement determination time (t1), the second bed-entrance determination condition being a condition according to which it is determined that the person has gotten into bed if the amplitude of the biological information signal (S2) continues to exceed a biological information threshold (V2) for at least a bed-entrance biological-information determination time (t2).Linvention concerne une section de détection de signal biologique (41) qui permet de détecter un signal dinformation biologique (S2) (par exemple le signal dun rythme cardiaque) ayant une amplitude qui change en fonction de lactivité biologique dune personne allant au lit. En outre, une section détection de signal de mouvement du corps (20, 33) permet de détecter un signal de mouvement du corps (S1) ayant une amplitude qui change en fonction de la magnitude du mouvement du corps de ladite personne. En outre, une section détermination (44) permet de déterminer que la personne sest mise au lit si une première condition de détermination de mise au lit et/ou une seconde condition de détermina
