Previously, when workpieces were passed from the preceding process, they were pooled until a batch was ready for processing. This slide tray oven enables heat treatment of workpieces as they come, on each slide tray, sending workpieces to the next process with minimal lost time. Additionally, this model can perform heat treatment for small-volume workpieces for the necessary time on each tray, which also minimizes the drop in temperature when door is opened as well as allowing faster recovery of the processing temperature, both of which contributes to better utilization rate in the heat treatment process.