Hinge module including detent structure and foldable electronic device including the hinge module

An electronic device comprising:

• a foldable housing including:
• a hinge structure,
• a first housing structure connected to the hinge structure, the first housing structure including a first surface and a second surface opposite to the first surface,
• a second housing structure connected to the hinge structure, the second housing structure including a third surface and a fourth surface opposite to the third surface, and
• a hinge housing,
• wherein the first housing structure is foldable about the hinge structure with the second housing structure,
• wherein in a folded state, the first surface faces the third surface, and in an unfolded state, the first surface and the third surface face the same direction, and
• wherein between the folded state and the unfolded state, the first housing structure is rotatable about a first axis extending along the hinge structure, and the second housing structure is rotatable about a second axis parallel to the first axis;
• a flexible display including a first area disposed on the first housing structure and a second area disposed on the second housing structure, wherein the first area and the second area form the first surface and the third surface;
• and
• a first detent structure disposed in the hinge housing, wherein the first detent structure includes:
• a first member connected to the first housing structure, the first member including a first through-hole and a second through-hole that are aligned along a third axis that is spaced apart from and parallel to the first axis and the second axis,
• a second member connected with the second housing structure and formed to receive part of the first member in the unfolded state, the second member including a first recess or a first opening configured to face the first through-hole and a second recess or a second opening configured to face the second through-hole,
• a first ball coupled with the first through-hole and disposed between the first through-hole and the first recess or the first opening in the unfolded state,
• a second ball coupled with the second through-hole and disposed between the second through-hole and the second recess or the second opening in the unfolded state, and
• a first elastic member located in the first member between the first ball and the second ball and configured to press the first ball and the second ball outward.