A sheet processing apparatus comprising: a conveyance unit (14A-14D) that in use conveys a sheet in a first direction; at least one of sheet processing units (46A, 46B) that is movable along one movement path extending in a second direction intersecting the first direction in plan view of the sheet; a guide member (70A-70C) that in use supports the sheet from below, the guide member (70A-70C) including a fixed end that is at least rotatable about a rotation center line extending in a vertical direction and disposed at a position out of the movement path; and a biasing member that in use biases the guide member (70A-70C) so as to return to an original orientation in which a part of the guide member (70A-70C) is located on the movement path; characterized in that the sheet processing apparatus further comprises: a controller that in use controls movement of the sheet processing units (46A, 46B); and a collision determination unit that in use determines, before the controller moves at least one of the sheet processing units (46A, 46B) and based on a movement start position and a target position of a sheet processing unit (46A, 46B) which is the target of the movement and a size and an orientation of the guide member (70A-70C) before start of the movement, whether or not there is a possibility of occurrence of collision of the sheet processing unit (46A, 46B) which is the target of the movement with the guide member (70A-70C) in a rotating state. a conveyance unit (14A-14D) that in use conveys a sheet in a first direction; at least one of sheet processing units (46A, 46B) that is movable along one movement path extending in a second direction intersecting the first direction in plan view of the sheet; a guide member (70A-70C) that in use supports the sheet from below, the guide member (70A-70C) including a fixed end that is at least rotatable about a rotation center line extending in a vertical direction and disposed at a position out of the movement path; and a biasing member that in use biases the guide member (70A-70C) so as to return to an original orientation in which a part of the guide member (70A-70C) is located on the movement path; characterized in that the sheet processing apparatus further comprises: a controller that in use controls movement of the sheet processing units (46A, 46B); and a collision determination unit that in use determines, before the controller moves at least one of the sheet processing units (46A, 46B) and based on a movement start position and a target position of a sheet processing unit (46A, 46B) which is the target of the movement and a size and an orientation of the guide member (70A-70C) before start of the movement, whether or not there is a possibility of occurrence of collision of the sheet processing unit (46A, 46B) which is the target of the movement with the guide member (70A-70C) in a rotating state. a controller that in use controls movement of the sheet processing units (46A, 46B); and a collision determination unit that in use determines, before the controller moves at least one of the sheet processing units (46A, 46B) and based on a movement start position and a target position of a sheet processing unit (46A, 46B) which is the target of the movement and a size and an orientation of the guide member (70A-70C) before start of the movement, whether or not there is a possibility of occurrence of collision of the sheet processing unit (46A, 46B) which is the target of the movement with the guide member (70A-70C) in a rotating state.