A blower is disposed in a main flow passage of a main unit of a CPAP device. An upstream flow passage connected upstream of the main flow passage is in a base unit. A sealing member secured to the base unit of the CPAP device has an annular shape surrounding a second outlet from outside. The shape of an opening of the sealing member at a distal end edge in the extending direction is a shape surrounding a first inlet from outside. The dimension of the sealing member in the extending direction is greater than the dimension of the sealing member in the thickness direction. When the main unit is attached to the base unit, the dimension of the sealing member in the extending direction is greater than a minimum distance from a proximal end of the sealing member in the extending direction to the main unit.