The invention provides a gas-solid separator comprising: an inner cylinder (10) having a closed lower end (11) and an opened upper end (1), and extending in a vertical direction; and an outer cylinder (2) that coaxially covers the inner cylinder (10) from the outside and has a gas vent port (6) formed on the upper end side and communicating with an exterior, wherein a plurality of axially extending long holes (4) are formed on a side surface on the lower end 11 side of the inner cylinder (10) in a circumferential direction, one of long side edge parts of each of the long holes (4) is providedwith a guide blade (5) that protrudes outward and is inclined circumferentially so as to cover the long hole (4), and in a section of the outer cylinder (2) that surrounds the plurality of long holes(4) of the inner cylinder (10), an inner diameter (D1) of a lower part is larger than an inner diameter (D2) of an upper part.