A cab for a construction machine, comprising: an operator seat including a seat base and a backrest extending upward from the seat base ; a control box disposed along a lateral side of the operator seat ; an air conditioner main body for cooling an air; and a duct disposed behind the operator seat for guiding a cooling air generated in the air conditioner main body , wherein the control box has an inner surface extending in a front-rear direction along the seat base , the duct has a blowing port for blowing out the cooling air, and the blowing port is at such a position as to allow the cooling air blown out from the blowing port to flow frontward along at least one of a lateral side of the seat base and a lateral side of a lower portion of the backrest and along the inner surface (20R, of the control box , the cab further comprises an armrest including an armrest main body extending in the front-rear direction and a support member for supporting the armrest main body , the lower portion of the backrest is located below a top surface of the armrest main body , and in a side view, an upper end of the blowing port is located above a rear end of the seat base , characterized in that in the side view, a lower end of the blowing port is located below the top surface of the armrest main body , in a front view, an outer end of the blowing port is located at an outer position in the left-right direction than at least one of an outer side surface of the seat base and an outer side surface of the lower portion of the backrest , and in the front view, the inner end of the blowing port is located at an inner position in the left-right direction than a rear end of the inner surface of the control box . an operator seat including a seat base and a backrest extending upward from the seat base ; a control box disposed along a lateral side of the operator seat ; an air conditioner main body for cooling an air; and a duct disposed behind the operator seat for guiding a cooling air generated in the air conditioner main body , wherein the control box has an inner surface extending in a front-rear direction along the seat base , the duct has a blowing port for blowing out the cooling air, and the blowing port is at such a position as to allow the cooling air blown out from the blowing port to flow frontward along at least one of a lateral side of the seat base and a lateral side of a lower portion of the backrest and along the inner surface (20R, of the control box , the cab further comprises an armrest including an armrest main body extending in the front-rear direction and a support member for supporting the armrest main body , the lower portion of the backrest is located below a top surface of the armrest main body , and in a side view, an upper end of the blowing port is located above a rear end of the seat base , characterized in that in the side view, a lower end of the blowing port is located below the top surface of the armrest main body , in a front view, an outer end of the blowing port is located at an outer position in the left-right direction than at least one of an outer side surface of the seat base and an outer side surface of the lower portion of the backrest , and in the front view, the inner end of the blowing port is located at an inner position in the left-right direction than a rear end of the inner surface of the control box . <EOS>