A fixing device for fixing an unfixed toner image on a recording material while conveying and heating the recording material bearing the unfixed toner image at a nip portion, the fixing device comprising: a rotary member for contacting the unfixed toner image; a pressure member for forming the nip portion by contacting the rotary member; and a cover for covering the rotary member with a space between the rotary member and the cover, characterized in that: in a cross section of the fixing device, the cross section being orthogonal to a generatrix direction of the rotary member, assuming that H represents a shortest distance between the nip portion and a farthest surface portion of the rotary member farthest away from a surface portion forming the nip portion of the rotary member, W represents a maximum width of the rotary member in the conveyance direction of the recording material, S represents an area of the space in a range of the maximum width W in the cross section, su represents a shortest distance between an upstream cover portion of the cover, disposed upstream of the nip portion in the conveyance direction of the recording material, and a virtual line obtained by extending the nip portion to an upstream side of the nip portion in the conveyance direction of the recording material, and ka represents a shortest distance between the upstream cover portion and a surface portion of the rotary member on the upstream side of the nip portion in the conveyance direction of the recording material, S, W, H, su and ka satisfy with a relationship of S / W ≥ 0.7 × H; su ≤ H / 2; and ka ≤ 5 mm. a rotary member for contacting the unfixed toner image; a pressure member for forming the nip portion by contacting the rotary member; and a cover for covering the rotary member with a space between the rotary member and the cover, characterized in that: in a cross section of the fixing device, the cross section being orthogonal to a generatrix direction of the rotary member, assuming that H represents a shortest distance between the nip portion and a farthest surface portion of the rotary member farthest away from a surface portion forming the nip portion of the rotary member, W represents a maximum width of the rotary member in the conveyance direction of the recording material, S represents an area of the space in a range of the maximum width W in the cross section, su represents a shortest distance between an upstream cover portion of the cover, disposed upstream of the nip portion in the conveyance direction of the recording material, and a virtual line obtained by extending the nip portion to an upstream side of the nip portion in the conveyance direction of the recording material, and ka represents a shortest distance between the upstream cover portion and a surface portion of the rotary member on the upstream side of the nip portion in the conveyance direction of the recording material, S, W, H, su and ka satisfy with a relationship of S / W ≥ 0.7 × H; su ≤ H / 2; and ka ≤ 5 mm. in a cross section of the fixing device, the cross section being orthogonal to a generatrix direction of the rotary member, assuming that H represents a shortest distance between the nip portion and a farthest surface portion of the rotary member farthest away from a surface portion forming the nip portion of the rotary member, W represents a maximum width of the rotary member in the conveyance direction of the recording material, S represents an area of the space in a range of the maximum width W in the cross section, su represents a shortest distance between an upstream cover portion of the cover, disposed upstream of the nip portion in the conveyance direction of the recording material, and a virtual line obtained by extending the nip portion to an upstream side of the nip portion in the conveyance direction of the recording material, and ka represents a shortest distance between the upstream cover portion and a surface portion of the rotary member on the upstream side of the nip portion in the conveyance direction of the recording material, S, W, H, su and ka satisfy with a relationship of S / W ≥ 0.7 × H; su ≤ H / 2; and ka ≤ 5 mm.