A thin-section preparation method for preparing a thin section by cutting an embedded block, in which a biological sample is embedded, a first cutting blade and a second cutting blade, held by a holder, each cutting blade having a blade edge and being long in a blade edge direction, the holder holding detachably the first and the second cutting blades in a state where the blade edge is exposed to an outside, the thin-section preparation method comprising: a cutting blade switching of switching between a one-blade set state and a two-blade set state of the holder, holder having a width equal to the length of the cutting blades (121a, 121b) in the blade edge direction, the first and the second cutting blades having the same length in the blade edge direction, the one-blade set state being a state in which the entire first cutting blade, which includes a first end region and a second end region along a blade edge direction, is held by the holder while the first end region and the second end region of the first cutting blade are held by the holder, the two-blade set state being a state in which the second end region of the first cutting blade and a third end region of the second cutting blade, which includes the third end region and a fourth end region along the blade edge direction, are held by the holder, the one-blade set state being switched to the two-blade set state by pushing out along the blade edge direction the first end region of the first cutting blade from the holder in the one-blade set state with the third end region of the second cutting blade, a first rough cutting step of performing rough cutting of the embedded block in the first end region of the first cutting blade, in the one-blade set state; a first main cutting step of performing main cutting of the embedded block on which the first rough cutting step has been performed in the second end region of the first cutting blade, in the one-blade set state; the cutting blade switching step being performed after the first main cutting step; a second rough cutting step of performing rough cutting of the embedded block in the second end region of the first cutting blade used in the first main cutting step, in the two-blade set state; and a second main cutting step of performing main cutting of the embedded block on which the second rough cutting step has been performed in the third end region of the second cutting blade in the two-blade set state. a cutting blade switching of switching between a one-blade set state and a two-blade set state of the holder, holder having a width equal to the length of the cutting blades (121a, 121b) in the blade edge direction, the first and the second cutting blades having the same length in the blade edge direction, the one-blade set state being a state in which the entire first cutting blade, which includes a first end region and a second end region along a blade edge direction, is held by the holder while the first end region and the second end region of the first cutting blade are held by the holder, the two-blade set state being a state in which the second end region of the first cutting blade and a third end region of the second cutting blade, which includes the third end region and a fourth end region along the blade edge direction, are held by the holder, the one-blade set state being switched to the two-blade set state by pushing out along the blade edge direction the first end region of the first cutting blade from the holder in the one-blade set state with the third end region of the second cutting blade, a first rough cutting step of performing rough cutting of the embedded block in the first end region of the first cutting blade, in the one-blade set state; a first main cutting step of performing main cutting of the embedded block on which the first rough cutting step has been performed in the second end region of the first cutting blade, in the one-blade set state; the cutting blade switching step being performed after the first main cutting step; a second rough cutting step of performing rough cutting of the embedded block in the second end region of the first cutting blade used in the first main cutting step, in the two-blade set state; and a second main cutting step of performing main cutting of the embedded block on which the second rough cutting step has been performed in the third end region of the second cutting blade in the two-blade set state.