Sense-B-noise is a rare cause of inappropriate shock (IAS) of subcutaneous implantable cardioverter defibrillator (S-ICD), which is an oversensing of primary and alternate vectors using the sense B and a factor of non-cardiac signal oversensing. The mechanism of sense-B-noise is unclear and considered to be a malfunction of the sense B circuit, including the ring and lead. We present a case of a 47-year-old man, who experienced IAS of S-ICD due to sense-B-noise followed by intense noise of primary and alternate vectors. This case implied that the mechanism of sense-B-noise may be an initial sign of malfunction of the sense B circuit.