A measuring device includes a support frame, a distance sensor and display (DSD), and a measuring arm. The support frame includes a first support arm, a linking rod, a poke rod, an elastic member, and a second support arm. The DSD includes a movable measuring head. A fixed measuring head is arranged coaxially with the movable measuring head to measure a distance between them. The poke rod includes a poke portion and a resisting portion. When the poke portion is pulled towards the first support arm, the resisting portion can resist against the linking rod, and the linking rod rotates to move the measuring heads.