To maximize the efficiency of utilization of mother substrates used as material for the substrates in the flat display panel to form a display screen, the flat display panel includes a display screen formed by tetragonal first and second substrates. Four sides or opposite two sides forming a tetragonal peripheral edge of the first substrate are rendered to be substantially equal to those of the second substrate, and the first and second substrate are sandwiched together with one of the first and second substrates protruding in part outwardly from the peripheral edge of the other of the first and second substrates.