A cab includes a driver's seat for an operator to sit and an air conditioner in its internal space. A floor plate forming the floor includes a tapered portion on a front side with respect to an operator sitting on the driver's seat and a rectangular portion on a rear side with respect to the operator as seen in a plan view, and the tapered portion is in a tapered trapezoidal shape having two parallel sides and a dimension in a width direction decreasing frontward. A through hole is formed in the floor plate of a region of the tapered portion and connects the internal space of the cab and an external space of the cab to each other. Accordingly, the pressure in the cab can effectively be reduced.