Image forming device that detects a state of an image carrier

An image forming device that forms a latent image on a rotating cylindrical image carrier, comprising:

• a conductive roller that abuts the image carrier to rotate;
• a power supply circuit that applies voltage to the roller;
• a controller that controls the power supply circuit so as to apply the voltage to the roller over a predetermined detection period in a state in which the image carrier and the roller are rotated;
• a detection value acquirer that acquires a detection value acquired by the application of the voltage indicating a state of the image carrier every cycle shorter than a time in which the roller rotates once in the detection period;
• and
• a state detector that detects a state of the image carrier on the basis of a plurality of acquired detection values,
• wherein a length of the detection period is set to a length at which both the numbers of rotations of the image carrier and the roller from a start of the detection period are integers.