A data transform method comprises a linear transform step of acquiring 16 linear Hadamard transform coefficients by multiplying the 16 pieces of data by an Hadamard transform matrix, an offset step of classifying the 16 linear Hadamard transform coefficients into four groups, each group containing an odd number of coefficients, and adding a predetermined offset value to linear Hadamard transform coefficients in every group, and an integral step of acquiring the lossless Hadamard transform coefficients by truncating decimal fractions down from a decimal point from the linear Hadamard transform coefficients added said predetermined offset value. With this configuration, a 16-point lossless Hadamard transform is implemented using only one rounding process.