A manufacturing method of an ultrasonic generating device, the method comprising: attaching an attachment unit to a bar portion of a bolt-shaped member from a second axial direction side, the attachment unit including a piezoelectric element (29A-29C) configured to convert a current to an ultrasonic vibration, a head portion forming a first end of the bolt-shaped member on a first axial direction side, the first axial direction being a direction parallel to a longitudinal axis of the ultrasonic generating device, the bar portion smaller in an outside diameter than the head portion forming a second end of the bolt-shaped member on the second axial direction side, the second axial direction being opposite to the first axial direction; characterized in that the method further comprises fixing, as a fixed end, the second end of the bolt-shaped member to which the attachment unit is attached, by using a bolt fixing portion (53;73;96) of a jig (51;71), while the bolt-shaped member is expandable by a movement of the first end which is a free end toward the first axial direction; applying a compressive force to the attachment unit toward the first axial direction by a force applying unit (60; 80) while the second end of the bolt-shaped member is fixed and thereby contracting the attachment unit, and expanding the bolt-shaped member by a first elastic force of the contracted attachment unit; and attaching a fastening member (43; 97) to the bar portion of the bolt-shaped member in a balanced condition in which a second elastic force of the expanded bolt-shaped member and the first elastic force of the attachment unit are in balance, and fastening the attachment unit between the fastening member (43; 97) and the head portion of the bolt-shaped member to maintain the balanced condition. attaching an attachment unit to a bar portion of a bolt-shaped member from a second axial direction side, the attachment unit including a piezoelectric element (29A-29C) configured to convert a current to an ultrasonic vibration, a head portion forming a first end of the bolt-shaped member on a first axial direction side, the first axial direction being a direction parallel to a longitudinal axis of the ultrasonic generating device, the bar portion smaller in an outside diameter than the head portion forming a second end of the bolt-shaped member on the second axial direction side, the second axial direction being opposite to the first axial direction; characterized in that the method further comprises fixing, as a fixed end, the second end of the bolt-shaped member to which the attachment unit is attached, by using a bolt fixing portion (53;73;96) of a jig (51;71), while the bolt-shaped member is expandable by a movement of the first end which is a free end toward the first axial direction; applying a compressive force to the attachment unit toward the first axial direction by a force applying unit (60; 80) while the second end of the bolt-shaped member is fixed and thereby contracting the attachment unit, and expanding the bolt-shaped member by a first elastic force of the contracted attachment unit; and attaching a fastening member (43; 97) to the bar portion of the bolt-shaped member in a balanced condition in which a second elastic force of the expanded bolt-shaped member and the first elastic force of the attachment unit are in balance, and fastening the attachment unit between the fastening member (43; 97) and the head portion of the bolt-shaped member to maintain the balanced condition.