PURPOSE: To obtain a sandwich-structural panel within a short time by simple bonding work using a specific one-pack type moisture-curable urethane adhesive in the bonding of surface materials and a core material.

CONSTITUTION: In preparing a sandwich-structural panel by using a weighed base material as a core material and bonding surface plates to the core material, an one- pack type moisture-curable urethane adhesive containing 0.1-6wt.% of isocyanate as the solid conversion value of an entire adhesive also compounded with various additives, having a mean MW of 8000-50000 and showing heat activity at 70°C or higher is applied to the single surfaces of the surface plates and the surface plates are pressed to the core material for several sec by a heating press and for several sec by a cooling press to be bonded thereto. When a prepolymer whose mean MW is less than 8000-50000 is applied, it runs off without being sufficiently bonded and, when the prepolymer whose mean MW is more than 8000-50000 is applied, coating workability is bad because of high solution viscosity and low solid content. When isocyanate content is less than 1-6wt.% as the solid conversion value in the entire adhesive, sufficient crosslinking curing is not performed and, when said content is larger than 1-6wt.%, sufficient curing is not performed only by the moisture in the base material.