PURPOSE: To provide a spacer with little pressure drop for fuel bundle of boiling water nuclear reactor.

CONSTITUTION: A cell spacer arrangement for enclosing a fuel bundle B within a channel in a prescribed height position is formed of cells of a first layer L1 for enclosing alternate fuel rods within the row and column of fuel rod matrix in the first height position L1 of a spacer S1, cells of a second layer L2 for enclosing the remaining alternate fuel rods of the fuel rod row and column in a second height position L2, and a means for connecting the first layer and the second layer to integrate the both. Since the height of each cell is a half of that in prior arts, the pressure drop is consequently halved in the first height position, and the remaining half pressure drop is caused in the second height position since the spacer projecting area is a half of that in prior arts. No cell is present just near the horizontal direction of a flow resistance generated in one layer, and the cells in one layer never cause an interaction with the passage friction.