A wiring board (1, 1a, 20, 20a) having: a board body (2, 22) including an insulating material and having a front surface (3, 23), a back surface (4, 24), a cavity (5, 25) having an opening in the front surface (3, 23) of the board body (2, 22) and having a bottom surface (6, 26) and a side surface (7, 27), and a projection which is provided on a front surface side of the side surface (7, 27) of the cavity and projects toward a center of the opening; a metal layer (11) provided on the side surface (7, 27) of the cavity; and an insulating portion which is provided on a back surface (9, 29) of the projection (8, 28) so as to define an obtuse angle (θ) with the metal layer (11), or which covers at least a top end portion of the metal layer (11).