PURPOSE: To provide a reflow soldering device which is proper for soldering of a high density mounting substrate whereon a part of a large heat capacity is mounted.

CONSTITUTION: A reflow soldering device is constituted of a pre-heating part 2, a reflow part 3, a cooling part 4 and a local heating part 6 for an auxiliary heating provided to the pre-heating part 2. When a printed substrate 5a whereon a part of a large heat capacity is carried by a conveyor 1 and reaches the local heating part 6, the conveyor 1 stops temporarily and near infrared beam is radiated from a heat source 8a of the local heating device 6 toward a part of a large heat capacity of the printed substrate 5a for local heating. An entire of a substrate becomes heated in a pre-heating part 2 before the printed substrate 5a reaches the local heating part 6, and it is additionally heated successively in heated state. Therefore, a uniform pre-heating temperature can be attained in a short time.