In a core bit formed with a drill portion in a cylindrical shape formed with a boring blade on one end side thereof and a mounting portion in a cylindrical shape mounted to a chuck portion of a concrete drill on other end side of the drill portion, formed with an engaging portion capable of being engaged with an engaging portion on a side of the chuck portion at an outer peripheral face of the mounting portion for transmitting rotation of a side of the concrete drill via the engaging member, the outer peripheral face of the mounting portion on a side of the boring blade of the engaging member is formed with a flange portion in a shape of a flange having a diameter larger than an outer diameter of the engaging member.
