A development aid device for development of a ladder program such as a user program for a programmable controller has a program memory for storing the user program and an outline data generating part for sequentially scanning constituent elements of this stored user program to extract specified elements including output commands and generating outline data by assigning individual index numbers to these extracted elements sequentially in the order of their appearance on the user program. An outline data memory stores the generated outline data. A cross-reference data generating part generates cross-reference data by extracting commands having a same operand from the user program, and a cross-reference data memory stores the generated cross-reference data. A display device is provided with a user program display area for displaying the user program, an outline data display area for displaying the generated outline data in a tree form in the order of appearance, and a cross-reference data display area for displaying the cross-reference data.