A flame-retardant rubber composition for vulcanization, comprising an epichlorohydrin based rubber, red phosphorus, and a vulcanizing agent, in which the content of the red phosphorus is from 3 to 20 parts by weight for 100 parts by weight of the epichlorohydrin based rubber. To deter dirt particles from proceeding to electronic components, the cooling structure can include a second flow channel, which starts from a port oriented transversely to the first flow direction or away therefrom and receives part of the flow from the inlet, and which conveys the part of the flow to an electronic component located in the second flow channel. A magnet is also provided, the magnet having a magnetic force.