A paper cutter capable of cutting a paper with a width of a margin of the paper adjusted arbitrarily, wherein a fixed blade is provided at an end of a paper mounting base, a guide rail is disposed on a rear face side of the fixed blade, a slider is disposed slidably on the guide rail, a rotary blade holder having a rotary circular blade and an arm are attached to a mobile member, the arm disposed striding over the fixed blade, a paper pressing plate pressing portion for pressing a paper pressing plate disposed such that it is capable of approaching/leaving the fixed blade is attached to the arm, and a scale for adjusting the width of the margin to be formed on a periphery of a cutting object paper is formed in the paper pressing plate in parallel to a cutting line.