Up io the present day many kinds of mathematical discussions on incompressible viscous fluid motion have fully developed (cf. [32,36] Now in the present paper, we shall show that the first initial-boundary value problem for it can uniquely be solved under suitable assumptions for the initial-boundary data and for the boundary of the domain, from the classical point of view.In § 1 an exact statement and the main theorem (Theorem 1) will be found. In §2 we perform the characteristic transformation and mention the theorem of the transformed problem (Theorem 2). Firstly we prove Theorem 2 and then show that Theorem 2 implies Theorem 1 in the last section § 8. In § § 3-5 linear equations connected with the transformed equations are treated. In more detail, in § 3. 1 we briefly state some basic results for a fundamental solution in the whole space R s due to Eidel'man [9,18] [1, 10-12, 14, 15, 22, 29-31, 54].We estimate the Green matrix in § 4 and the solution in § 5. Making use of these results we give a proof of the existence in § 6 by the method of successive approximation and that of the uniqueness in § 7, therefore the proof of Theorem 2 is completed.Acknowledgement. Deep gratitude is due to Professor N. Itaya