A muscle building tool 1 is used to build, by applying a predetermined pressure to at least one of a user's four limbs to restrict blood flow, a muscle of the limb, and includes: a belt 10 that is wrapped around the at least one of the four limbs and applies the pressure to the muscle； a fastener 40 that maintains a loop shape of the belt 10 in a state of applying the pressure to the muscle； a tension sensor 60 that measures a tension acting on the belt 10 when wrapping the belt 10； and a pressure sensor that is configured to automatically start an operation when the tension measured by the tension sensor 60 exceeds a predetermined threshold, and measures the pressure applied to the muscle.
