A digital power amplifier has first and second switches, between a high potential power line and a low potential power line, which operate complementarily. A node of the radio interference suppression capacitor 2 and the power supply holding switch 4 is connected via an auxiliary power line 1d to a primary side terminal 7a of a stepdown transformer 7, and another primary side terminal 7b of the stepdown transformer 7 is connected to a power line 1b. A switch means is provided between the bit line BL and local bit line LBL connected to the memory cells for isolation and coupling of these bit lines.