A fixing device which fixes an image on a recording medium, the fixing device comprising: an endless fixing rotary member formed into a loop and configured to come into contact with the image carried on the recording medium; an opposed rotary member configured to be in contact with the fixing rotary member; a nip forming member provided inside the loop formed by the fixing rotary member to be in contact with the opposed rotary member via the fixing rotary member to form, between the fixing rotary member and the opposed rotary member, a nip portion to which the recording medium is fed in a feeding direction; a support member configured to support the nip forming member; and a heating source configured to heat the fixing rotary member, wherein the heating source heats a portion of the fixing rotary member other than a portion of the fixing rotary member corresponding to the nip portion, characterized in that the nip forming member includes a base pad and a sliding sheet, provided on at least a surface of the base pad configured to face the inner surface of the fixing rotary member, the base pad subjected to pressure applied by the opposed rotary member, wherein a surface of the base pad on the side of the opposed rotary member includes a contact portion, an extended portion and a curved portion, wherein the contact portion is formed in a substantially flat surface in contact with the opposed rotary member via the fixing rotary member, wherein the nip forming member has a first length of an upstream portion extending upstream in the sheet feeding direction from a center of the nip portion and a second length of a downstream portion extending downstream in the sheet feeding direction from the center of the nip portion, wherein the first length is longer than the second length. an endless fixing rotary member formed into a loop and configured to come into contact with the image carried on the recording medium; an opposed rotary member configured to be in contact with the fixing rotary member; a nip forming member provided inside the loop formed by the fixing rotary member to be in contact with the opposed rotary member via the fixing rotary member to form, between the fixing rotary member and the opposed rotary member, a nip portion to which the recording medium is fed in a feeding direction; a support member configured to support the nip forming member; and a heating source configured to heat the fixing rotary member, wherein the heating source heats a portion of the fixing rotary member other than a portion of the fixing rotary member corresponding to the nip portion, characterized in that the nip forming member includes a base pad and a sliding sheet, provided on at least a surface of the base pad configured to face the inner surface of the fixing rotary member, the base pad subjected to pressure applied by the opposed rotary member, wherein a surface of the base pad on the side of the opposed rotary member includes a contact portion, an extended portion and a curved portion, wherein the contact portion is formed in a substantially flat surface in contact with the opposed rotary member via the fixing rotary member, wherein the nip forming member has a first length of an upstream portion extending upstream in the sheet feeding direction from a center of the nip portion and a second length of a downstream portion extending downstream in the sheet feeding direction from the center of the nip portion, wherein the first length is longer than the second length.