An illumination system includes: a first light-emitting element column in which one or more first light-emitting elements are serially connected; a second light-emitting element column connected in parallel with the first light-emitting element column, and in which one or more second light-emitting elements are serially connected; a constant current supply that supplies constant current to a light source unit including the first and second light-emitting element columns; a resistor that is connected in series with the first light-emitting element column, and detects magnitude of current flowing through at least the first light-emitting element column; a bypass circuit that passes, to the resistor, at least part of current flowing through the second light-emitting element column, when a predetermined condition is satisfied; and a current adjuster circuit that adjusts the magnitude of the current flowing through the first light-emitting element column, according to the magnitude of the current detected by the resistor.