A trigger signal generating device includes a first power source terminal and a second power source terminal; a first current generator to generate a first current with a first amplitude in accordance with the amplitude of the input signal; a second current generator to generate a second current with a second amplitude, the second current being flowed from the first power source terminal to the second power source terminal; a current mirror circuit to amplify the second current generated from the second current generator to obtain an amplified current; and a trigger signal generator to convert the amplified current into a trigger signal used for triggering a trigger device, the voltage amplitude of the trigger signal being corresponding to the current amplitude of the amplified current; wherein both of the first and second current generators are connected to either one of the first and second power source terminals.