A lamp body lighting system for a vehicle, comprising: a lamp body unit comprising: a plurality of lamp bodies, each lamp body comprising two turn signal lamps (15a1, 15a2; 15a3, 15a4), which are connected in parallel with each other; and a lamp body control apparatus that is outside the lamp body unit and that is configured to light the plurality of lamp bodies by supplying a current through a drive current path to said lamp bodies, and that is further configured to receive a voltage from an electric source of the vehicle for supplying the current; the lamp body control apparatus comprising a breaking detection part configured to detect a breaking of each of the plurality of lamp bodies, and the breaking detection part comprises: a shunt resistance provided in the drive current path which supplies the current to said plurality of lamp bodies; characterized in that the lamp body lighting system further comprises a plurality of constant current circuits (40a1, 40a2; 40b1, 40b2), each constant current circuit being connected in series with a respective one of said turn signal lamps and each constant current circuit controlling the current flowing through the current path of its respective turn signal lamp to be constant; a breaking determination section that uses a predetermined threshold value to determine that one of the plurality of lamp bodies is broken when a potential difference between both terminals of the shunt resistance is less than the predetermined threshold value, whereby the predetermined threshold value is based on a value of current in a stable zone in which the current through the drive current path is constant even when the voltage received by the lamp body control apparatus varies, said value of current in the stable zone is between a value of current flowing through the drive current path that supplies the plurality of lamp bodies when only any one of the two turn signal lamps of a respective lamp body is lighted and a value of current flowing through the drive current path that supplies the plurality of lamp bodies when both of the two turn signal lamps of the respective lamp body are lighted. a lamp body unit comprising: a plurality of lamp bodies, each lamp body comprising two turn signal lamps (15a1, 15a2; 15a3, 15a4), which are connected in parallel with each other; and a lamp body control apparatus that is outside the lamp body unit and that is configured to light the plurality of lamp bodies by supplying a current through a drive current path to said lamp bodies, and that is further configured to receive a voltage from an electric source of the vehicle for supplying the current; the lamp body control apparatus comprising a breaking detection part configured to detect a breaking of each of the plurality of lamp bodies, and the breaking detection part comprises: a shunt resistance provided in the drive current path which supplies the current to said plurality of lamp bodies; characterized in that the lamp body lighting system further comprises a plurality of constant current circuits (40a1, 40a2; 40b1, 40b2), each constant current circuit being connected in series with a respective one of said turn signal lamps and each constant current circuit controlling the current flowing through the current path of its respective turn signal lamp to be constant; a breaking determination section that uses a predetermined threshold value to determine that one of the plurality of lamp bodies is broken when a potential difference between both terminals of the shunt resistance is less than the predetermined threshold value, whereby the predetermined threshold value is based on a value of current in a stable zone in which the current through the drive current path is constant even when the voltage received by the lamp body control apparatus varies, said value of current in the stable zone is between a value of current flowing through the drive current path that supplies the plurality of lamp bodies when only any one of the two turn signal lamps of a respective lamp body is lighted and a value of current flowing through the drive current path that supplies the plurality of lamp bodies when both of the two turn signal lamps of the respective lamp body are lighted. a shunt resistance provided in the drive current path which supplies the current to said plurality of lamp bodies; characterized in that the lamp body lighting system further comprises a plurality of constant current circuits (40a1, 40a2; 40b1, 40b2), each constant current circuit being connected in series with a respective one of said turn signal lamps and each constant current circuit controlling the current flowing through the current path of its respective turn signal lamp to be constant; a breaking determination section that uses a predetermined threshold value to determine that one of the plurality of lamp bodies is broken when a potential difference between both terminals of the shunt resistance is less than the predetermined threshold value, whereby the predetermined threshold value is based on a value of current in a stable zone in which the current through the drive current path is constant even when the voltage received by the lamp body control apparatus varies, said value of current in the stable zone is between a value of current flowing through the drive current path that supplies the plurality of lamp bodies when only any one of the two turn signal lamps of a respective lamp body is lighted and a value of current flowing through the drive current path that supplies the plurality of lamp bodies when both of the two turn signal lamps of the respective lamp body are lighted.