A wearable instrument is provided that measures biological information over an extended period of time by enabling an electrode to be readily pressed to an axilla of an animal. The wearable instrument includes: electrodes to be placed under the left and right axillae of a dog to produce an electrocardiogram； pull-up straps to be placed in direct contact with the axilla to press the electrodes onto the axilla； and a cinch strap placed across the anterior chest of the dog to draw the left and right sections of the pull-up strap together.
