In a signal generating device 2, first signal generation means 12 for generating a most significant bit signal stream MSB, second signal generation means 13 for generating a least significant bit signal stream LSB, a mask generation means 14 for defining a bit that allows error insertion and a bit that prohibits error insertion with different pieces of bit information, and generating a mask pattern of each of the most significant bit signal stream MSB and the least significant bit signal stream LSB, based on symbol transition information indicating a transition destination of four PAM4 symbols of a PAM4 signal; and error insertion means 15 for inserting an error, based on bit information of the mask pattern corresponding to each bit of the most significant bit signal stream and the least significant bit signal stream designated according to a symbol error rate.