To provide a portable electronic instrument capable of being installed using an instrument mounting stand, and being readily installed at an angle easily seen even at a stationary place without receiving vibrations such as the outside of a vehicle.

In this portable electronic instrument 1 formed of a flat casing 2 with a display screen 3, the casing 2 is provided with an rotary arm 4 with its one end rotatably connected to the central part of the back surface of the casing 2 for supporting the casing 2 when it is placed on a placing surface. Moreover, in the central part of the rotary arm 4, a connection groove 6 mountable in the instrument mounting stand is formed.