PURPOSE: To provide a clock signal generating circuit to be used for obtaining a measuring instrument capable of using rapid and synchronizing signals simultaneously with other plural measuring instruments.

CONSTITUTION: The clock signal generating circuit to be used for a measuring instrument for measuring an electric signal such as a digital oscilloscope is characteristically provided with a pull-up input terminal 2, an input buffer 3 for amplifying an input signal inputted from the input terminal 2, a crystal oscillation circuit 1 for inputting a signal from the buffer 3 through a coupling capacitor 5, an output buffer 6 for amplifying a signal outputted from the circuit 1, and an output terminal 7 for outputting a signal obtained from the buffer 6 to the external.