Efficiency of producing polycrystalline silicon is improved. A silicon filament (11) is constituted by a rod-shaped member made of polycrystalline silicon. The polycrystalline silicon has an interstitial oxygen concentration of not less than 10 ppma and not more than 40 ppma. On a side surface, in a lengthwise direction, of the rod-shaped member, crystal grains each having a crystal grain size of not less than 1 mm are observed.