The knee-protecting airbag of the present invention is folded and housed in front of knees of a seated vehicle occupant for protecting the knees, and includes an airbag body and a tether. The airbag body includes an occupant's side wall located toward the occupant upon deployment and a vehicle body side wall located toward the vehicle body. A lower part of the airbag body serves as an upstream, and an upper part of the airbag body serves as a downstream, respectively of flowing-in inflation gas. The tether has a band shape arranged along the transverse direction, and joins the walls, such that passages for gas are formed between the left and right ends of the tether and the left and right edges of the airbag in the inner circumference of the airbag body. The tether includes a gas communication hole. The gas communication hole is so dislocated from the transverse center of the airbag as to face the transverse center of the seated occupant.