A large thin wall superconducting solenoid magnet was constructed as a major component of the high energy particle detector 'TOPAZ' for the TRISTAN e** plus e** minus collider at KEK. A newly developed 'internal winding method' was an essential technique to fabricate a large coil as thin as possible. The magnet has been successfully tested with iron return yoke. It has been cooled down to 4. 5 K and excited up to the rated current of 3650 A with a magnetic field of 1. 21 T. Results of the tests and preliminary analyses are reported.