A combustion apparatus with an air supply chamber in a lower part partitioned by a partition plate from an arrangement section of a burner unit and a primary air chamber in a front part stands from a front end of the air supply chamber are provided in a combustion housing incorporating the burner unit. Air from a combustion fan connected to an air supply port of the air supply chamber flows to the primary air chamber through the air supply chamber. Primary air is supplied from the primary air chamber to burners of the burner unit. Projected rims extend from the periphery of a portion of the partition plate opposed to the air supply port to a front edge of the partition plate are provided on a lower surface of the partition plate. The height of a downward projection of the projected rims is reduced toward the air supply port.