PURPOSE: To provide the power source control circuit of a speech synthesizer which converts the data obtd. from an IC card attachably and detachably inserted to a body to speech.

CONSTITUTION: This power source control circuit is constituted of a detecting switch 10 to be closed when the IC card 2 is held mounted to the body, a control transistor 12 to be biased to a conducting state when this detecting switch 10 is held closed, a transistor 11 for power source supply to be biased to the conducting state and to supply the power source to a speech synthesizing circuit 5 which performs a speech synthesis operation when this control TR 12 is in the conducting state and a control circuit 6 for detecting the opening and closing state of the detecting switch 10 and for controlling the operation of the control TR 12.