A knee airbag device includes an airbag module and an airbag door. The airbag module includes a gas generation device that is operated when the knee airbag device is operated, and a knee airbag that is stored in a folded state inside a column cover that covers the rear end portion of a steering column. When the knee airbag receives gas from the gas generation device, the knee airbag is inflated and deployed toward the knee of an occupant. The airbag door, provided in the lower portion of the column cover, is made of a flexible material. When the knee airbag is inflated and deployed, the airbag door is opened toward the knee of the occupant due to an airbag inflation pressure.