A bolt includes a body and a detecting portion. The body includes a shank and a head provided at one end of the shank. The detecting portion is configured to detect a strain in accordance with an axial force of the shank. The detecting portion includes a memory, a measuring portion, and a transmitting portion. The measuring portion is configured to operate by receiving a first wireless power feed, convert the strain into measurement data, and write the measurement data to the memory. The transmitting portion is configured to operate by receiving a second wireless power feed after the first wireless power feed, read the measurement data stored in the memory, and transmit the read measurement data.