To provide a fastening structure of a foamed resin core composite plate which can be applicable to both bolt fastening and resistance welding, and can keep rigid fastening to a member at the other end over a long period of time.

A through hole 2 and a crushed marginal part 3a formed by crushing a core material formed of a resin foam 1c at the periphery are provided in a fastening part of a foamed resin core composite plate 1. A vertical wall 4 in a shape of a tube rising from the peripheral edge of the through hole 2 is provided in the crushed marginal part 3a. A tubular part 11a of a metal fastening member 11 is inserted into the vertical wall 4 from the base end side with its seat 11b abutting on the crushed marginal part 3a. A grommet-like member 12 is put on the outside of the vertical wall 4. The front end side of the tubular part 11a protruding from the front end side of the vertical wall 4 is pressed and expanded so as to be swaged to the front end side of the vertical wall 4 with the grommet-like member 12 between. The fastening member 11 is fastened to a member A at the other end with a bolt 13 inserted in the tubular part 11a and a nut 14 so that the fastening member 11 is fastened to the member A at the other end by bolt connection.