Height adjustable armrest assembly and chair including the same

A chair comprising:

• a seating plate part on which a user sits;
• a pair of armrest assemblies which is provided at both left and right portions of the seating plate part and on which the user's arm is placed;
• and
• a backrest part having an upper end portion provided to tilt around a lower end portion in a front-rear direction on a rear end portion of the seating plate part,
• wherein the pair of armrest assemblies include:
• a fixing bracket part fixed to the both left and right end portions of the seating plate part and having an inner space that is open upward;
• and
• a lifting part provided to move vertically on an upper portion of the fixing bracket part,
• the lifting part includes:
• a lifting box provided to move vertically in the inner space of the fixing bracket part;
• a lifting body formed integrally on the lifting box;
• a lifting button part installed so that a portion is exposed outward from the lifting body and pushed and rotated by an external force provided by a user;
• a rotating lock part locked to or unlocked from the fixing bracket part in conjunction with the lifting button part;
• and
• a lifting connection member connecting the lifting connection member to the rotating lock part, and
• the rotating lock part has a lock pin locked to or unlocked from the fixing bracket part formed to protrude toward a front end portion of the lifting body.