A dryer comprising: a drum ; a wireless sensing device disposed in and configured to move freely around the drum and comprising: a sensing module including a humidity sensor configured to measure humidity in the drum , and an acceleration sensor , a sensor communication module configured to transmit or receive data through wireless communication, a sensor controller configured to control the sensor communication module to transmit a humidity value corresponding to an output of the humidity sensor, and a sensor power supplier configured to supply power to the sensing module , the sensor communication module , and the sensor controller ; a main communication module configured to receive the humidity value from the wireless sensing device ; and a main controller configured to determine that drying is completed when the humidity value is equal to or less than a set threshold, wherein the acceleration sensor is configured to measure acceleration while being rotated along with the drum , wherein the sensor controller is configured to control the sensor communication module to transmit an acceleration value corresponding to an output of the acceleration sensor , and wherein the main controller is configured to determine at least one of a load of laundry contained in the drum, or determine whether laundry contained in the drum is entangled, based on the acceleration value. a drum ; a wireless sensing device disposed in and configured to move freely around the drum and comprising: a sensing module including a humidity sensor configured to measure humidity in the drum , and an acceleration sensor , a sensor communication module configured to transmit or receive data through wireless communication, a sensor controller configured to control the sensor communication module to transmit a humidity value corresponding to an output of the humidity sensor, and a sensor power supplier configured to supply power to the sensing module , the sensor communication module , and the sensor controller ; a sensing module including a humidity sensor configured to measure humidity in the drum , and an acceleration sensor , a sensor communication module configured to transmit or receive data through wireless communication, a sensor controller configured to control the sensor communication module to transmit a humidity value corresponding to an output of the humidity sensor, and a sensor power supplier configured to supply power to the sensing module , the sensor communication module , and the sensor controller ; a main communication module configured to receive the humidity value from the wireless sensing device ; and a main controller configured to determine that drying is completed when the humidity value is equal to or less than a set threshold, wherein the acceleration sensor is configured to measure acceleration while being rotated along with the drum , wherein the sensor controller is configured to control the sensor communication module to transmit an acceleration value corresponding to an output of the acceleration sensor , and wherein the main controller is configured to determine at least one of a load of laundry contained in the drum, or determine whether laundry contained in the drum is entangled, based on the acceleration value. <EOS>