A respiration assistance device comprising: a nasal respiration assisting section for supplying a gas to a nasal cavity of a living body, wherein the nasal respiration assisting section includes: a first gas supplying portion which is configured by an opening of a fluid path for supplying the gas below and toward one of the nostrils of the living body, a second gas supplying portion which is configured by an opening of the fluid path for supplying the gas below and toward the other nostril of the living body, a first tube connecting portion to which a tube for supplying the gas to the first gas supplying portion is connected, and a second tube connecting portion to which a tube for supplying the gas to the second gas supplying portion is detachably connected; and further comprising a bite block which is detachably attached to the nasal respiration assisting section, and which is to be attached to an oral cavity of the living body, wherein the bite block includes: a wall surface portion which has an approximately tubular shape, an oral cavity contacting portion which is disposed on an outer surface of the wall surface portion, and which is to be contacted with the oral cavity that is opened, a through hole which is disposed in an inner surface of the wall surface portion, and into which a tubular article is insertable, a third gas supplying portion which is disposed in the through hole, and which supplies the gas to the oral cavity, and a third tube connecting portion to which a tube that supplies the gas to the third gas supplying portion is connectable. wherein the nasal respiration assisting section includes: a first gas supplying portion which is configured by an opening of a fluid path for supplying the gas below and toward one of the nostrils of the living body, a second gas supplying portion which is configured by an opening of the fluid path for supplying the gas below and toward the other nostril of the living body, a first tube connecting portion to which a tube for supplying the gas to the first gas supplying portion is connected, and a second tube connecting portion to which a tube for supplying the gas to the second gas supplying portion is detachably connected; and a first gas supplying portion which is configured by an opening of a fluid path for supplying the gas below and toward one of the nostrils of the living body, a second gas supplying portion which is configured by an opening of the fluid path for supplying the gas below and toward the other nostril of the living body, a first tube connecting portion to which a tube for supplying the gas to the first gas supplying portion is connected, and a second tube connecting portion to which a tube for supplying the gas to the second gas supplying portion is detachably connected; and further comprising a bite block which is detachably attached to the nasal respiration assisting section, and which is to be attached to an oral cavity of the living body, wherein the bite block includes: a wall surface portion which has an approximately tubular shape, an oral cavity contacting portion which is disposed on an outer surface of the wall surface portion, and which is to be contacted with the oral cavity that is opened, a through hole which is disposed in an inner surface of the wall surface portion, and into which a tubular article is insertable, a third gas supplying portion which is disposed in the through hole, and which supplies the gas to the oral cavity, and a third tube connecting portion to which a tube that supplies the gas to the third gas supplying portion is connectable. a wall surface portion which has an approximately tubular shape, an oral cavity contacting portion which is disposed on an outer surface of the wall surface portion, and which is to be contacted with the oral cavity that is opened, a through hole which is disposed in an inner surface of the wall surface portion, and into which a tubular article is insertable, a third gas supplying portion which is disposed in the through hole, and which supplies the gas to the oral cavity, and a third tube connecting portion to which a tube that supplies the gas to the third gas supplying portion is connectable.