A gas-solid separator has: 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 of the inner cylinder 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 provided with a guide blade 5 that protrudes outward and is inclined circumferentially so as to cover the long hole 4, and a part between the long holes 4 of the inner cylinder 10 is concaved in a center direction of the inner cylinder 10.