Hole drilling device for forming expanded-diameter hole portion

A hole drilling device for forming an expanded-diameter hole portion at an inner bottom part of a bottomed mounting hole formed in a drilling object, the hole drilling device comprising:

• a shaft including a contact surface and a tapered surface, the contact surface being formed on a front end portion of the shaft and coming into contact with the inner bottom part of the mounting hole, the tapered surface being formed on a side surface of the front end portion of the shaft and expanding toward the contact surface;
• a cutter including a cutting bit formed on a front end portion of the cutter, the cutter being externally attached to the shaft such that the cutter is slidable in a forward-rearward direction, the cutting bit being guided by the tapered surface and protruding laterally from the tapered surface when the cutter slides forward along the shaft;
• a shank coupled to the cutter and externally attached to the shaft, such that the shank is slidable in the forward-rearward direction;
• and
• a biasing element provided between the shank and the shaft, the biasing element configured to bias the shaft forward, wherein
• the cutter includes a stopper provided on a side surface of a rear end portion of the cutter, the stopper coming into contact with a surface of the drilling object when the cutter slides forward along the shaft, and
• a diameter of the stopper is formed to be larger than a diameter of a front end portion of the shank.