A diesel engine start-up assisting device includes a plurality of first-and-second switching elements 11a to 11d between a common direct-current power source 1 and a plurality of electrical load 3a to 3d, a plurality of start-up assisting main parts 10a to 10d and an input-and-output unit 7. The diesel engine start-up assisting device is constructed so as to enable start-up of a diesel engine when power distribution is applied to at least one of the electrical loads 3a to 3d. In arrangement, the first-and-second switching elements 11a to 11d, the start-up assisting main parts 10a to 10d and the input-and-output unit 7 are integrated into one package having a lead frame. Defining the first-and-second switching element as a pair of switching elements, the first-and-second switching elements 11a to 11d are arranged in parallel with each other on the lead frame, and the lead frame has a notch part formed between two pairs of switching elements adjoined to each other.