A developer carrying device comprising: a developer carrying unit configured to carry a developer containing a toner and a carrier in a rotation axis direction while agitating the developer with rotation of an agitating and carrying member; and a toner-concentration detecting unit configured to detect a toner concentration in the developer carried in the developer carrying unit, wherein the developer carrying unit further comprises a side plate (21K-3) and a partition wall (21K-5), wherein a pressing wall is configured to bridge the side plate (21K-3) and the partition wall (21K-5) of the developer carrying unit in a developer carrying direction in the developer carrying unit, the pressing wall coming into contact with, from above in the gravity direction, the developer that moves from a lower side to an upper side in the gravity direction according to the rotation of the agitating and carrying member and pressing the developer downward in the gravity direction, wherein the pressing wall is opposed to a bottom wall (21K-6) of the developer carrying unit on a lower side in a gravity direction of the agitating and carrying member and opposed to the side plate (21K-3) and the partition wall (21K-5) of the developer carrying unit on both lateral sides orthogonal to the rotation axis direction of the agitating and carrying member, and the toner concentration of the developer being carried is detected by the toner-concentration detecting unit, wherein the agitating and carrying member includes a screw member including a rotatably-supported rotation shaft member and a spiral blade protrudingly provided in a spiral shape on a peripheral surface of the rotation shaft member, wherein a reverse carrying blade, that carries the developer in a direction opposite to a carrying direction of the spiral blade according to the rotation of the rotation shaft member, is protrudingly provided in an area opposite to the pressing wall in the entire area in the rotation axis direction in the rotation shaft member, characterized in that the reverse carrying blade is provided between two opposed surfaces of the spiral blade, in that gaps are provided between the opposed surfaces of the spiral blade and the reverse carrying blade, respectively, and when the reverse carrying blade passes the area opposed to the toner-concentration detecting unit, a pressing force of the developer applied to the toner-concentration detecting unit is the largest. a developer carrying unit configured to carry a developer containing a toner and a carrier in a rotation axis direction while agitating the developer with rotation of an agitating and carrying member; and a toner-concentration detecting unit configured to detect a toner concentration in the developer carried in the developer carrying unit, wherein the developer carrying unit further comprises a side plate (21K-3) and a partition wall (21K-5), wherein a pressing wall is configured to bridge the side plate (21K-3) and the partition wall (21K-5) of the developer carrying unit in a developer carrying direction in the developer carrying unit, the pressing wall coming into contact with, from above in the gravity direction, the developer that moves from a lower side to an upper side in the gravity direction according to the rotation of the agitating and carrying member and pressing the developer downward in the gravity direction, wherein the pressing wall is opposed to a bottom wall (21K-6) of the developer carrying unit on a lower side in a gravity direction of the agitating and carrying member and opposed to the side plate (21K-3) and the partition wall (21K-5) of the developer carrying unit on both lateral sides orthogonal to the rotation axis direction of the agitating and carrying member, and the toner concentration of the developer being carried is detected by the toner-concentration detecting unit, wherein the agitating and carrying member includes a screw member including a rotatably-supported rotation shaft member and a spiral blade protrudingly provided in a spiral shape on a peripheral surface of the rotation shaft member, wherein a reverse carrying blade, that carries the developer in a direction opposite to a carrying direction of the spiral blade according to the rotation of the rotation shaft member, is protrudingly provided in an area opposite to the pressing wall in the entire area in the rotation axis direction in the rotation shaft member, characterized in that the reverse carrying blade is provided between two opposed surfaces of the spiral blade, in that gaps are provided between the opposed surfaces of the spiral blade and the reverse carrying blade, respectively, and when the reverse carrying blade passes the area opposed to the toner-concentration detecting unit, a pressing force of the developer applied to the toner-concentration detecting unit is the largest.