A biological information measuring device includes: a light-emitting unit emitting irradiation light irradiating an arm； a light-receiving unit receiving reflected light of the irradiation light reflected off the arm； a passage part where the irradiation light and the reflected light pass； and a back lid having a contact surface which surrounds the passage part and comes into contact with the arm, the back lid supporting the passage part. The passage part has an outer surface part coming into contact with the arm, and an inner surface part in a front-back relationship with the outer surface part. The outer surface part has a convex surface protruding from the contact surface and along a first direction from the light-emitting unit toward the passage part and coming into contact with the arm. The inner surface part has a recess part having a bottom surface provided between the contact surface and the convex surface as viewed along a cross section taken from a second direction orthogonal to the first direction.
