Electric circuit breaker device

An electric circuit breaker comprising:

• a housing serving as an outer shell member and including an accommodating space extending in one direction;
• an igniter provided in the housing;
• a projectile disposed in the housing and configured to be projected from an end side of the accommodating space by energy received from the igniter and move along an extension direction of the accommodating space;
• and
• a conductor piece held by the housing and forming a part of an electric circuit, the conductor piece including a cutoff portion disposed crossing the accommodating space between a first connecting end portion and a second connecting end portion and configured to be cut off by movement of the projectile, wherein,
• in the accommodating space, a region defined by an inner wall of the housing holding the conductor piece serves as a holding region,
• the projectile includes a rod portion extending along the extension direction of the accommodating space and inserted into the holding region,
• the rod portion includes a widened portion having a cross-sectional area orthogonal to an axial direction of the rod portion increasing from a tip end side toward a rear end side in the axial direction, and
• the widened portion includes an interference fit portion that is interference-fitted by coming into contact with the inner wall of the housing defining the holding region when the projectile is projected.