A sheet processing apparatus, comprising: a creasing unit arranged to form a crease (S-C) on a sheet; a support arranged to support the sheet on which the crease (S-C) has been formed by the creasing unit; a folding roller arranged to fold the sheet supported by the support while rotating at a folding speed; characterized by further comprising: a thrusting member arranged to move at a thrust speed, which is higher than the folding speed, and to thrust the sheet supported by the support towards the folding roller such that the sheet on which the crease (S-C) has been formed is folded by the folding roller at a position where the crease (S-C) has been formed; and a control unit arranged to control the thrusting member and the folding roller such that a speed difference between a folding speed of the folding roller and a thrust speed of the thrusting member, in a case in which the folding roller folds a first number of sheets including the sheet on which the crease (S-C) has been formed, is smaller than a speed difference between the folding speed of the folding roller and the thrust speed of the thrusting member, in a case in which the folding roller folds a second number of sheets, the second number of sheets being larger than the first number of sheets, including the sheet on which the crease (S-C) has been formed. a creasing unit arranged to form a crease (S-C) on a sheet; a support arranged to support the sheet on which the crease (S-C) has been formed by the creasing unit; a folding roller arranged to fold the sheet supported by the support while rotating at a folding speed; characterized by further comprising: a thrusting member arranged to move at a thrust speed, which is higher than the folding speed, and to thrust the sheet supported by the support towards the folding roller such that the sheet on which the crease (S-C) has been formed is folded by the folding roller at a position where the crease (S-C) has been formed; and a control unit arranged to control the thrusting member and the folding roller such that a speed difference between a folding speed of the folding roller and a thrust speed of the thrusting member, in a case in which the folding roller folds a first number of sheets including the sheet on which the crease (S-C) has been formed, is smaller than a speed difference between the folding speed of the folding roller and the thrust speed of the thrusting member, in a case in which the folding roller folds a second number of sheets, the second number of sheets being larger than the first number of sheets, including the sheet on which the crease (S-C) has been formed. a thrusting member arranged to move at a thrust speed, which is higher than the folding speed, and to thrust the sheet supported by the support towards the folding roller such that the sheet on which the crease (S-C) has been formed is folded by the folding roller at a position where the crease (S-C) has been formed; and a control unit arranged to control the thrusting member and the folding roller such that a speed difference between a folding speed of the folding roller and a thrust speed of the thrusting member, in a case in which the folding roller folds a first number of sheets including the sheet on which the crease (S-C) has been formed, is smaller than a speed difference between the folding speed of the folding roller and the thrust speed of the thrusting member, in a case in which the folding roller folds a second number of sheets, the second number of sheets being larger than the first number of sheets, including the sheet on which the crease (S-C) has been formed.