An image forming apparatus comprising: an image carrying member on a surface of which an electrostatic latent image is formed; a magnetic roller which, by action of a magnet included therein, carries two-component developer containing toner and magnetic carrier in a form of a magnetic brush on a surface thereof and which, by rotating, transports the carried magnetic brush; a developing roller arranged opposite the image carrying member and opposite the magnetic roller, the developing roller carrying on a surface thereof the toner contained in the magnetic brush transported by rotation of the magnetic roller and feeding the carried toner to the image carrying member; and a restricting member arranged under the developing roller at a predetermined interval from the magnetic roller, the restricting member restricting a layer thickness of the developer on the surface of the magnetic roller, a first voltage application section for applying a first bias to the magnetic roller; a second voltage application section for applying a second bias to the developing roller; and a controller (132, 160) including: a drive circuit which drives a developing motor which makes the magnetic roller and the developing roller rotate; and a control section which feeds the drive circuit with a forward direction signal or a reverse direction signal, characterized in that the controller is adapted to execute, when no image formation is taking place, a toner collection mode in which, with the first and second biases set at a same potential and the second bias set lower than a voltage applied to the image carrying member, the magnetic roller is rotated in a direction reverse to a direction in which the magnetic roller is rotated during image formation and to keep, in the toner collection mode, the developing roller stationary, and between the developing motor and the developing roller, a one-way clutch is provided which prevents the developing roller from rotating in a reverse direction, the drive circuit drives the developing motor in response to the reverse direction signal, the magnetic roller is driven by the developing motor to rotate in the direction reverse to the direction in which it rotates during image formation, and the developing roller is prevented by the one-way clutch from rotating in the reverse direction. an image carrying member on a surface of which an electrostatic latent image is formed; a magnetic roller which, by action of a magnet included therein, carries two-component developer containing toner and magnetic carrier in a form of a magnetic brush on a surface thereof and which, by rotating, transports the carried magnetic brush; a developing roller arranged opposite the image carrying member and opposite the magnetic roller, the developing roller carrying on a surface thereof the toner contained in the magnetic brush transported by rotation of the magnetic roller and feeding the carried toner to the image carrying member; and a restricting member arranged under the developing roller at a predetermined interval from the magnetic roller, the restricting member restricting a layer thickness of the developer on the surface of the magnetic roller, a first voltage application section for applying a first bias to the magnetic roller; a second voltage application section for applying a second bias to the developing roller; and a controller (132, 160) including: a drive circuit which drives a developing motor which makes the magnetic roller and the developing roller rotate; and a control section which feeds the drive circuit with a forward direction signal or a reverse direction signal, a drive circuit which drives a developing motor which makes the magnetic roller and the developing roller rotate; and a control section which feeds the drive circuit with a forward direction signal or a reverse direction signal, characterized in that the controller is adapted to execute, when no image formation is taking place, a toner collection mode in which, with the first and second biases set at a same potential and the second bias set lower than a voltage applied to the image carrying member, the magnetic roller is rotated in a direction reverse to a direction in which the magnetic roller is rotated during image formation and to keep, in the toner collection mode, the developing roller stationary, and between the developing motor and the developing roller, a one-way clutch is provided which prevents the developing roller from rotating in a reverse direction, the drive circuit drives the developing motor in response to the reverse direction signal, the magnetic roller is driven by the developing motor to rotate in the direction reverse to the direction in which it rotates during image formation, and the developing roller is prevented by the one-way clutch from rotating in the reverse direction.