This paper presents an experimental study on the interaction of twin turbulent circular jet. The velocity and the static pressure of the jets were measured by varying the distance between two nozzles. The results of the twin-jet were compared with those of a jet parallel to a plane wall on the basis of the principle of reflected image. The main results are as follows : (1) The twin-jet interacts and joints in the form of an ellipse at the downstream distance, becoming close to a circular jet at far downstream distance. (2) The position of maximum velocity of the twin-jet shifts from the axis of nozzle to the mid-point between the jets. (3) The positions of maximum velocity of the twin-jet and the jet parallel to a plane wall are expressed by similar curves for various nozzle distances. (4) The difference between the characteristics of the twin-jet and those of the jet parallel to a plate wall is due to their different boundary conditions.