The present disclosure herein relates to a biosignal detecting device and a biosignal detecting system including the same. According to an embodiment of the inventive concept, the biosignal detecting device is built in a vehicle seat. The biosignal detecting device includes an antenna block. The antenna block transmits a transmission signal to a person seated on the vehicle seat and receives a return signal corresponding to the transmission signal. The antenna block and one surface contacting the seated person are spaced apart from each other so that a distance therebetween is two times or more greater than a wavelength of the transmission signal. According to an embodiment of the inventive concept, through an optimized arrangement of the biosignal detecting device, the biosignal of the seated person may be exactly and effectively detected.