A turn signal device to be provided in a host vehicle for indicating an advancement direction of the host vehicle to an exterior of the host vehicle, comprising: a right turn signal, to be provided on a right side of a rear part of the host vehicle, the right turn signal having a plurality of light-emitting units (24A-24D, 25A-25D) arranged in a vehicle width direction of the host vehicle; a left turn signal, to be provided on a left side of the rear part of the host vehicle, the left turn signal having a plurality of light-emitting units (24A-24D, 25A-25D) arranged in the vehicle width direction of the host vehicle; an operation device, to be provided in a driver cab of the host vehicle, the operation device being capable of generating an operation signal for causing one or both of the right turn signal and the left turn signal to operate in response to an operation made by a driver; an acquisition unit that is configured to acquire a determination signal indicating a determination result of whether or not there is a risk of a collision between the host vehicle and a following vehicle traveling behind the host vehicle; a normal situation control unit that, on the basis of the operation signal, outputs a normal situation control signal such that the plurality of light-emitting units (24A-24D, 25A-25D) in one or both of the right turn signal and the left turn signal light up sequentially from an inner side to an outer side with respect to the vehicle width direction; and a dangerous situation control unit that, upon the determination signal indicating a determination result that there is a risk of the collision being acquired, outputs a dangerous situation control signal such that the plurality of light-emitting units (24A-24D, 25A-25D) in both of the right turn signal and the left turn signal light up sequentially from the outer side to the inner side with respect to the vehicle width direction, wherein the normal situation control unit outputs the normal situation control signal such that after a first light-emitting unit lights up, a subsequent adjacent light-emitting unit of the plurality of light-emitting units lights up while the first light-emitting unit remains lit, and the dangerous situation control unit outputs the dangerous situation control signal such that for each turn signal (21, 22) after a first light-emitting unit lights up, a subsequent adjacent light-emitting unit of the plurality of light-emitting units lights up while the first light-emitting unit remains lit. a right turn signal, to be provided on a right side of a rear part of the host vehicle, the right turn signal having a plurality of light-emitting units (24A-24D, 25A-25D) arranged in a vehicle width direction of the host vehicle; a left turn signal, to be provided on a left side of the rear part of the host vehicle, the left turn signal having a plurality of light-emitting units (24A-24D, 25A-25D) arranged in the vehicle width direction of the host vehicle; an operation device, to be provided in a driver cab of the host vehicle, the operation device being capable of generating an operation signal for causing one or both of the right turn signal and the left turn signal to operate in response to an operation made by a driver; an acquisition unit that is configured to acquire a determination signal indicating a determination result of whether or not there is a risk of a collision between the host vehicle and a following vehicle traveling behind the host vehicle; a normal situation control unit that, on the basis of the operation signal, outputs a normal situation control signal such that the plurality of light-emitting units (24A-24D, 25A-25D) in one or both of the right turn signal and the left turn signal light up sequentially from an inner side to an outer side with respect to the vehicle width direction; and a dangerous situation control unit that, upon the determination signal indicating a determination result that there is a risk of the collision being acquired, outputs a dangerous situation control signal such that the plurality of light-emitting units (24A-24D, 25A-25D) in both of the right turn signal and the left turn signal light up sequentially from the outer side to the inner side with respect to the vehicle width direction, wherein the normal situation control unit outputs the normal situation control signal such that after a first light-emitting unit lights up, a subsequent adjacent light-emitting unit of the plurality of light-emitting units lights up while the first light-emitting unit remains lit, and the dangerous situation control unit outputs the dangerous situation control signal such that for each turn signal (21, 22) after a first light-emitting unit lights up, a subsequent adjacent light-emitting unit of the plurality of light-emitting units lights up while the first light-emitting unit remains lit.