An automatic fire alarm system master device configured to transmit signals to a plurality of slave devices (10, B1-B16) electrically connected to a pair of cables (51, 52), a voltage being applied to the pair of cables (51, 52), the automatic fire alarm system master device comprising: a transmitter electrically connected to the pair of cables (51, 52) and configured to transmit the signals to the plurality of slave devices (10, B1-B16) by varying the voltage between the pair of cables (51, 52); a transmission controller configured to control the transmitter to have a synch signal (SY1, SY11, SY12) transmitted from the transmitter every time a predetermined amount of time passes; a receiver electrically connected to the pair of cables (51, 52) and configured to receive signals from the plurality of slave devices (10, B1-B16) in accordance with a variation in the voltage between the pair of cables (51, 52); a reception controller configured to control the receiver; and a processor configured to acquire data included in response signals (SN1-SN16) from an output of the receiver, the plurality of slave devices (10, B1-B16) transmitting their respective response signals (SN1-SN16) by varying the voltage between the pair of cables (51, 52) after their respective waiting times (W1-W16) have passed since reception of the synch signal (SY1, SY11, SY12), the waiting times (W1-W16) varying their length from one of the plurality of slave devices (10, B1-B16) to another, the reception controller making the receiver receive the respective response signals (SN1-SN16) from the plurality of slave devices (10, B1-B16) during their respective reception periods (R21-R36) after the respective waiting times (W1-W16) have passed since transmission of the synch signal (SY1, SY11, SY12) by the transmitter, the predetermined amount of time being long enough to allow the response signals (SN1-SN16) to fall within the respective reception periods (R21-R36), characterized in that any two successive ones of the waiting times (W1-W16) of the plurality of slave devices (10, B1-B16) are different in length from each other by a constant time interval, each of the reception periods (R21-R36) is as long as the constant time interval, the processor is configured to regard, as noise, any surplus of the voltage between the pair of cables (51, 52) over a predetermined upper limit value in a vicinity of each of starting and ending timings of the reception periods (R21-R36), and is configured to distinguish the noise from the response signals (SN1-SN16), and/or the processor is configured to regard, as noise, any deficit in the voltage between the pair of cables (51, 52) under a predetermined lower limit value in a vicinity of each of starting and ending timings of the reception periods (R21-R36), and is configured to distinguish the noise from the response signals (SN1-SN16). a transmitter electrically connected to the pair of cables (51, 52) and configured to transmit the signals to the plurality of slave devices (10, B1-B16) by varying the voltage between the pair of cables (51, 52); a transmission controller configured to control the transmitter to have a synch signal (SY1, SY11, SY12) transmitted from the transmitter every time a predetermined amount of time passes; a receiver electrically connected to the pair of cables (51, 52) and configured to receive signals from the plurality of slave devices (10, B1-B16) in accordance with a variation in the voltage between the pair of cables (51, 52); a reception controller configured to control the receiver; and a processor configured to acquire data included in response signals (SN1-SN16) from an output of the receiver, the plurality of slave devices (10, B1-B16) transmitting their respective response signals (SN1-SN16) by varying the voltage between the pair of cables (51, 52) after their respective waiting times (W1-W16) have passed since reception of the synch signal (SY1, SY11, SY12), the waiting times (W1-W16) varying their length from one of the plurality of slave devices (10, B1-B16) to another, the reception controller making the receiver receive the respective response signals (SN1-SN16) from the plurality of slave devices (10, B1-B16) during their respective reception periods (R21-R36) after the respective waiting times (W1-W16) have passed since transmission of the synch signal (SY1, SY11, SY12) by the transmitter, the predetermined amount of time being long enough to allow the response signals (SN1-SN16) to fall within the respective reception periods (R21-R36), characterized in that any two successive ones of the waiting times (W1-W16) of the plurality of slave devices (10, B1-B16) are different in length from each other by a constant time interval, each of the reception periods (R21-R36) is as long as the constant time interval, the processor is configured to regard, as noise, any surplus of the voltage between the pair of cables (51, 52) over a predetermined upper limit value in a vicinity of each of starting and ending timings of the reception periods (R21-R36), and is configured to distinguish the noise from the response signals (SN1-SN16), and/or the processor is configured to regard, as noise, any deficit in the voltage between the pair of cables (51, 52) under a predetermined lower limit value in a vicinity of each of starting and ending timings of the reception periods (R21-R36), and is configured to distinguish the noise from the response signals (SN1-SN16).