A cover for an infant seat, comprising: (1) a flexible, bag-form main body having, in a top portion thereof, an opening for introducing therethrough an infant into the main body, and having a leg through-hole for allowing the leg of an infant to extend out of the main body, and (2) a flexible flap extending from a portion of the main body, which portion is positioned above the leg through-hole, wherein the flap has a free end, wherein when the flap is allowed to hang downwardly, the flap is engaged with the main body to close the leg through-hole, and wherein when the main body is installed on the seat in a manner such that the flap is placed on or wrapped around a support means provided on the seat for preventing the falling of an infant, the infant in the main body is prevented from directly contacting the support means.