To provide a plug insertable into a hole of a panel with low insertion resistance, and firmly engageable with the hole.

This plug 10 has a flange part 12 abutting on the surface side peripheral edge of the hole 3 arranged in the panel 1, a cylindrical outer peripheral wall 14 suspended from the inner periphery of the flange part 12, a bottom part 16 extended in the inner diameter direction from the lower end of the outer peripheral surface 14, a cylindrical inner peripheral wall 18 rising to the flange part 12 side from the inner periphery of the bottom part 16, a pressing part 20 connected to an upper end part of the inner peripheral wall 18, and an annular groove 22 formed between the outer peripheral wall 14 and the inner peripheral wall 18 and forming a shape of opening the flange part 12 side. The outer peripheral wall 14 is provided with a plurality of first locking parts 25 projected in the outer diameter direction at a predetermined interval in the peripheral direction and engaging with the back side peripheral edge of the hole 3, and a plurality of second locking parts 30 formed between these first locking parts 25, projected in the outer diameter direction in the height lower than the first locking parts 25 and engaging with the back side peripheral edge of the hole 3.