An easy-to-fit measuring instrument is provided. A measuring instrument (10) includes: a main wearable unit (1) to be fitted either to a neck of an animal on which measurement is to be made or close to the neck； and an electrode belt (5) including an electrode (6) to be fitted, for measurement of biological information, in such a manner that the electrode is in contact with at least either one of left and right axillae of the animal, wherein the electrode belt has a first end that is connected to the main wearable unit and a second end that is to be connected to the main wearable unit in a location that is closer to a back of the animal than the first end is close to the back of the animal.
