An electrical signal measuring device that can measure electrical characteristics of cells in culture in real time and with high accuracy while maintaining them in a favorable state and an electrical signal measuring method that uses the device are disclosed. The electrical signal measuring device 1 for cells in culture includes a support body 2, a compartment in the support body, a semipermeable membrane 3, and electrodes, in which the compartment is divided by the semipermeable membrane 3 into an upper compartment 4 and a lower compartment 5; an upper electrode 61 is provided in the upper compartment 4, and a lower electrode 62 that faces the upper electrode 61 and whose facing surface 621 is in contact with the semipermeable membrane 3 is provided in the lower compartment 5; and an upper perfusion channel and a lower perfusion channel are provided in the support body 2 to separately perfuse fluid in the upper compartment 4 and the lower compartment 5 is disclosed.