A temperature-compensated crystal oscillator includes a mode selector circuit 100, a control logic serial•interface 200, a PROM circuit 300, an oscillation control circuit 400 and an oscillation circuit 500, and has, as terminals, a power terminal (VCC/CLK) 11, an input terminal (VC/DATA/PE) 12, an output terminal (OUT) 13 and a ground terminal (GND) 14. The mode selector circuit 100 switches the crystal oscillator to an emulation mode when a first signal in which a power voltage and a clock signal supplied through the power terminal 11 are superimposed, is inputted from the power terminal and a second signal having a predetermined pattern is inputted from the input terminal 12.