A support tool is mounted on a finger of a subject on whom a sensor is mounted to support acquisition of biological information. A first support is disposed on a nail side of the subject's finger. A second support is disposed on a ventral side of the subject's finger. The relative position of the second support with respect to the first support does not change. A bag is formed with a material softer than the first support and second support, and is disposed along an inner peripheral face of the first support. A ventilation tube forms a ventilation channel communicating with an inside of the bag. The sensor includes a light emission part and a light reception part. The light emission part is disposed between the subject's finger and the bag. The light reception part is disposed between the subject's finger and the second support.