A biological sound sensor to be used in contact with a skin of a living body, and includes a casing that has an opening in a face on the side facing the skin of the living body, a double-sided adhesive membrane having a first surface and a second surface, the second surface closes the opening by adhering to the face of the casing and the first surface adheres to the skin when collecting a biological sound produced in the living body. A microphone is arranged in the casing and picks up the biological sound. The double-sided adhesive membrane has a one-material portion, made of the first adhesive material, through the double-sided adhesive membrane from the first surface to the second surface.
