A filament includes first and second end portions between which a connecting portion is arranged. The first and second end portions are electrically connected to a power supply device. The first end portion is bent with respect to the second end portion through the connecting portion. A cross-sectional dimension of the bent connecting portion is the same as cross-sectional dimensions of the first and second end portions. Also disclosed are an ionization chamber and an ion-implantation apparatus. The cross-sectional dimension of the filament is uniform. The resistance of respective portions of the filament is the same. The number of the hot electrons generated at respective portions by powering the filament is the same. The hot electrons and ion-source gas collide to generated plasma. The plasma concentration around the filament is uniform, to avoid the emergence of corrosion of the filament at certain portion caused by an over high plasma concentration.