To provide a power source adjusting device suitable for fixedly stabilizing power supply to a game machine such as a pachinko game stand from a power source transformer, and to provide a game machine power supply system using the device.

When a voltage drops in the power source transformer, a threshold voltage S3 is raised, the pulse width of a waveform adjusting pulse S5 is shortened, and the pulse width of the waveform S1 of a rectangular wave voltage is cut for the portion of the shortened pulse width. Consequently, the pulse width of the waveform S1 of the rectangular wave voltage to be supplied to the game machine is elongated immediately after the occurrence of the voltage drop in the power source transformer. Then an electric current is further supplied from the power source transformer to the game machine for the elongated portion compared with a case before the voltage drop.