Sheet folding device

An image forming apparatus, comprising:

• a printer to form an image on a printing medium;
• and
• a finisher to perform, after the image is formed on the printing medium, at least one of a stapling operation, an alignment operation, or a folding operation, the finisher including a sheet folding device which includes:
• a folding roller comprising at least two rollers that rotate and engage with each other to form a folding nip,
• a folding blade movable to an insertion location of the folding nip at which the printing medium, disposed on a folding path, is to be inserted into the folding nip, and to a retreat location to escape from the folding path, and
• a guide member including an inclined portion to form an acute angle with the folding blade to press the printing medium at the insertion location of the folding nip towards the folding roller when the folding blade reaches the insertion location of the folding nip,
• the guide member elastically biased by an elastic member and located at at least one side of the folding blade to move together with the folding blade and to press, by the inclined portion, the printing medium at the insertion location of the folding nip towards the folding roller, when the folding blade reaches the insertion location of the folding nip to insert the printing medium into the folding nip,
• the elastic member to apply an elastic force to the guide member towards the folding roller to press the printing medium at the insertion location of the folding nip toward the folding roller.