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 (20A, 20B) 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 (20A, 20B) has an inner surface (20R, 20L) extending in a front-rear direction along the seat base, the duct has a blowing port (41, 42) for blowing out the cooling air, and the blowing port (41, 42) is at such a position as to allow the cooling air blown out from the blowing port (41, 42) 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 (20A, 20B), the cab further comprises an armrest (27A, 27B) 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 (41, 42) is located above a rear end of the seat base, characterized in that in the side view, a lower end of the blowing port (41, 42) is located below the top surface of the armrest main body, in a front view, an outer end of the blowing port (41, 42) is located at an outer position in the left-right direction than at least one of an outer side surface (18AL, 18AR) of the seat base and an outer side surface (18BL, 18BR) of the lower portion of the backrest, and in the front view, the inner end of the blowing port (41, 42) is located at an inner position in the left-right direction than a rear end of the inner surface (20R, 20L) of the control box (20A, 20B). an operator seat including a seat base and a backrest extending upward from the seat base; a control box (20A, 20B) 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 (20A, 20B) has an inner surface (20R, 20L) extending in a front-rear direction along the seat base, the duct has a blowing port (41, 42) for blowing out the cooling air, and the blowing port (41, 42) is at such a position as to allow the cooling air blown out from the blowing port (41, 42) 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 (20A, 20B), the cab further comprises an armrest (27A, 27B) 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 (41, 42) is located above a rear end of the seat base, characterized in that in the side view, a lower end of the blowing port (41, 42) is located below the top surface of the armrest main body, in a front view, an outer end of the blowing port (41, 42) is located at an outer position in the left-right direction than at least one of an outer side surface (18AL, 18AR) of the seat base and an outer side surface (18BL, 18BR) of the lower portion of the backrest, and in the front view, the inner end of the blowing port (41, 42) is located at an inner position in the left-right direction than a rear end of the inner surface (20R, 20L) of the control box (20A, 20B).