A vehicle system comprising: a vehicle that travels on a trolley section by receiving electric power received from a trolley and travels on a trolleyless section using electric power from a battery unit mounted on the vehicle, the vehicle comprising: the battery unit serving as a power source in a trolleyless section; a charging disconnector and a discharging disconnector for changing over a charging/discharging state of the battery unit; a pair of contactors (10; 11) provided in positive and negative sides of the battery unit; a plurality of relays interlocking with open/close operations of each of the charging disconnector, the discharging disconnector, and the pair of contactors (10; 11); an open/close instructing portion that issues open/close instructions for the charging disconnector, the discharging disconnector, and the pair of contactors (10; 11); a diagnosis start determination portion that determines a diagnosis start timing before entering a trolleyless section; a remaining battery capacity check portion operated when the diagnosis start determination portion determines that it is a diagnosis start timing, the remaining battery capacity check portion checking whether or not the battery unit has a battery capacity necessary in a trolleyless section travel; a relay operation check portion that checks operability of the charging disconnector, the discharging disconnector, and the pair of contactors (10; 11) based on certain open/close states of the plurality of relays depending on the open/close instructions from the open/close instructing portion; and an abnormality determination portion that determines that the trolleyless section travel is not allowed when the relay operation check portion is incapable of checking the operability or the necessary remaining battery capacity, the remaining battery capacity check portion, the relay operation check portion, and the abnormality determination portion being operated when the diagnosis start determination portion determines that it is the diagnosis start timing. the battery unit serving as a power source in a trolleyless section; a charging disconnector and a discharging disconnector for changing over a charging/discharging state of the battery unit; a plurality of relays interlocking with open/close operations of each of the charging disconnector, the discharging disconnector, and the pair of contactors (10; 11); an open/close instructing portion that issues open/close instructions for the charging disconnector, the discharging disconnector, and the pair of contactors (10; 11); a diagnosis start determination portion that determines a diagnosis start timing before entering a trolleyless section; a remaining battery capacity check portion operated when the diagnosis start determination portion determines that it is a diagnosis start timing, the remaining battery capacity check portion checking whether or not the battery unit has a battery capacity necessary in a trolleyless section travel; a relay operation check portion that checks operability of the charging disconnector, the discharging disconnector, and the pair of contactors (10; 11) based on certain open/close states of the plurality of relays depending on the open/close instructions from the open/close instructing portion; and an abnormality determination portion that determines that the trolleyless section travel is not allowed when the relay operation check portion is incapable of checking the operability or the necessary remaining battery capacity, the remaining battery capacity check portion, the relay operation check portion, and the abnormality determination portion being operated when the diagnosis start determination portion determines that it is the diagnosis start timing.