According to one embodiment, a radio apparatus configured to communicate with a second radio apparatus after receiving plural first signals transmitted from the second radio apparatus in a constant cycle, the radio apparatus includes: a communication circuit configured to communicate with the second radio apparatus; a wave detection circuit configured to generate a wave detection signal by envelope-detecting the plural first signals; a bandpass filter having an IIR filter, configured to generate a detection signal form the wave detection signal, the detection signal having amplitude is increased at a frequency corresponding to the constant cycle; and a control unit configured to cause supply of power to the communication circuit if the amplitude is larger than a first threshold value.