Electric circuit breaker device

An electric circuit breaker device comprising:

• in a cylindrical space penetrating from a first end to a second end of a housing made of a synthetic resin, an igniter, a projectile made of a synthetic resin, and a conductor piece forming part of an electric circuit, which are arranged axially in this order from the first end of the housing;
• and having an insulating space for receiving a cut portion of the conductor piece between the second end of the housing and the conductor piece, wherein:
• the conductor piece is a plate piece comprising of connection sections at both ends thereof and a cutting section as an intermediate portion, and disposed so that the cutting section has a surface perpendicular to the axial direction of the housing;
• the projectile is disposed to face the surface of the cutting section of the conductor piece in the axial direction of the housing;
• a cylinder made of a metal for reinforcing the housing is disposed between the projectile and an inner wall surface of the housing;
• and
• the projectile has a constricted part fitted with an O-ring, the O-ring abuts against an inner periphery of the cylinder, and the projectile has an outer surface free from contact with the inner surface of the cylinder.