An apparatus that slices an embedded block having a biological sample embedded therein to prepare a thin section, includes: a cutter that slices the embedded block; a moving mechanism that relatively moves the block and the cutter along an approaching and separating direction in which they approach and separate from each other; a height adjusting mechanism that relatively moves them along a vertical direction; a sliding mechanism that relatively moves them along a sliding direction nearly orthogonal to the approaching and separating direction; and a control unit that controls them to begin to move at initial positions set in advance, the block to be brought into contact at the same point of a nose of the cutter, and the cutter to be slid in the same direction as a ratio between a velocity in the approaching and separating direction and a velocity in the sliding direction is kept the same.