An atomization unit, comprising: a tank formed in a bottomed cylindrical shape in which liquid is stored; and a holder fitted to an opening portion of the tank, wherein in a state in which the tank and the holder are fitted with each other, at least an engagement piece being elastically deformable towards inwardly in a radial direction is disposed in either of the tank or the holder to protrude from one of the tank and the holder positioned inwardly in the radial direction toward the other one of the tank and the holder, and an engagement portion being engageable with the engagement piece is disposed in the other one of the tank and the holder positioned outwardly in the radial direction, the atomization unit is characterized in that: the holder is fitted to an internal circumferential surface of the tank, an elastic applying member is formed in an internal surface at an internal side in the radial direction of the engagement piece so as to apply an elastic force outwardly in the radial direction to the engagement piece in response to an elastic deformation of the engagement piece inwardly in the radial direction, and the elastic applying member has a fitting portion to be fitted to an internal circumferential surface of the holder. a tank formed in a bottomed cylindrical shape in which liquid is stored; and a holder fitted to an opening portion of the tank, wherein in a state in which the tank and the holder are fitted with each other, at least an engagement piece being elastically deformable towards inwardly in a radial direction is disposed in either of the tank or the holder to protrude from one of the tank and the holder positioned inwardly in the radial direction toward the other one of the tank and the holder, and an engagement portion being engageable with the engagement piece is disposed in the other one of the tank and the holder positioned outwardly in the radial direction, at least an engagement piece being elastically deformable towards inwardly in a radial direction is disposed in either of the tank or the holder to protrude from one of the tank and the holder positioned inwardly in the radial direction toward the other one of the tank and the holder, and an engagement portion being engageable with the engagement piece is disposed in the other one of the tank and the holder positioned outwardly in the radial direction, the atomization unit is characterized in that: the holder is fitted to an internal circumferential surface of the tank, an elastic applying member is formed in an internal surface at an internal side in the radial direction of the engagement piece so as to apply an elastic force outwardly in the radial direction to the engagement piece in response to an elastic deformation of the engagement piece inwardly in the radial direction, and the elastic applying member has a fitting portion to be fitted to an internal circumferential surface of the holder. the holder is fitted to an internal circumferential surface of the tank, an elastic applying member is formed in an internal surface at an internal side in the radial direction of the engagement piece so as to apply an elastic force outwardly in the radial direction to the engagement piece in response to an elastic deformation of the engagement piece inwardly in the radial direction, and the elastic applying member has a fitting portion to be fitted to an internal circumferential surface of the holder.