A printer unit for an image forming apparatus, the printer unit having a printer module and an automatic cutting apparatus, the cutting apparatus comprising: a fixed blade module including a fixed blade; a movable blade module including a movable blade that moves when the movable blade module is driven; and a drive module configured to drive the movable blade module, wherein the fixed blade and the movable blade are configured to cut printed paper when the moveable blade slides, characterized in that: the fixed blade module, the movable blade module, and the drive module are connected in a mutually detachable state; a lock part of the fixed blade module is inserted into a lock part inserting part of the printer module, a positioning projection of the fixed blade module is inserted into a positioning projection inserting part of the printer module, and an engaging part of the fixed blade module engages an engaging part of the printer module in order to connect the fixed blade module and the printer module in an interfitted state; a rail of the drive module is inserted into a groove of the printer module and a spring-loaded lock part of the drive module engages an engaging part of the printer module in order to connect the drive module and the printer module in an interfitted state; and a bearing guide projection of the movable blade module is fitted into a bearing guide projection receiving part of the printer module and an inclination preventing stopper of the moveable blade module makes contact with a stopper engaging part of the printer module in order to connect the movable blade and the printer module in an interfitted state. a fixed blade module including a fixed blade; a movable blade module including a movable blade that moves when the movable blade module is driven; and a drive module configured to drive the movable blade module, wherein the fixed blade and the movable blade are configured to cut printed paper when the moveable blade slides, characterized in that: the fixed blade module, the movable blade module, and the drive module are connected in a mutually detachable state; a lock part of the fixed blade module is inserted into a lock part inserting part of the printer module, a positioning projection of the fixed blade module is inserted into a positioning projection inserting part of the printer module, and an engaging part of the fixed blade module engages an engaging part of the printer module in order to connect the fixed blade module and the printer module in an interfitted state; a rail of the drive module is inserted into a groove of the printer module and a spring-loaded lock part of the drive module engages an engaging part of the printer module in order to connect the drive module and the printer module in an interfitted state; and a bearing guide projection of the movable blade module is fitted into a bearing guide projection receiving part of the printer module and an inclination preventing stopper of the moveable blade module makes contact with a stopper engaging part of the printer module in order to connect the movable blade and the printer module in an interfitted state. the fixed blade module, the movable blade module, and the drive module are connected in a mutually detachable state; a lock part of the fixed blade module is inserted into a lock part inserting part of the printer module, a positioning projection of the fixed blade module is inserted into a positioning projection inserting part of the printer module, and an engaging part of the fixed blade module engages an engaging part of the printer module in order to connect the fixed blade module and the printer module in an interfitted state; a rail of the drive module is inserted into a groove of the printer module and a spring-loaded lock part of the drive module engages an engaging part of the printer module in order to connect the drive module and the printer module in an interfitted state; and a bearing guide projection of the movable blade module is fitted into a bearing guide projection receiving part of the printer module and an inclination preventing stopper of the moveable blade module makes contact with a stopper engaging part of the printer module in order to connect the movable blade and the printer module in an interfitted state.