A semiconductor storage device has a memory cell array, a plurality of word lines, a plurality of bit lines, and a plurality of blocks including a group of at least some memory cells, a defect information storage block that stores defect information in the memory cell array, a first defect detection circuitry that reads data of at least some memory cells in the defect information storage block, verifies the data, and determines whether there is a defect in the defect information storage block, a second defect detection circuitry that changes a read voltage level for reading the data of the memory cells, rereads data of at least some memory cells in the defect information storage block, verifies the data, and determines whether there is the defect in the defect information storage block, and a defect determination circuitry that determines the defect information storage block as a defective block.