A slitter for slitting a web 1 wound by an oscillation winding method includes a guide roller 2. The guide roller 2 has an axial length shorter than width of the web 1. The slitter includes guide means guiding the web 1 to engage the web with the guide roller 2. The web 1 includes widthwise opposite end portions of the web 1 protruding out of axial opposite end portions of the guide roller 2. The slitter includes slit blades 6 slitting the web 1 at positions of the axial opposite end portions of the guide roller 2.
