In the case of spray flash evaporation occurring in a superheated liquid jet ejected from a tubular nozzle into a low-pressure vapor zone when an aqueous NaCl solution is used as the working fluid for process steam generation and desalination, shattering of the jet into small droplets is rather restrained compared to that of water jet on condition that the superheat of the working fluid is less than 8 K, and it is conspicuous especially on condition that the superheat is less than 6 K when the working fluid flows as a liquid column confining vapor bubbles, resulting in the decrease of the evaporation efficiency. This paper describes the results of a thorough investigation to clarify the cause of the restraint of spray flash evaporation due to the presence of the non-volatile solute. Nucleated bubbles in the discharged jet come into contact with neighboring bubbles within an extremely short distance from the nozzle exit, and in the case of the working fluid containing the non-volatile solute, the boiling point at the bubble wall elevates considerably because the solute which is concentrated at the bubble wall as the bubble grows cannot diffuse due to the contact among the neighboring bubbles. As a result, the growth rate of the bubbles decreases leading to the restraint of evaporation at the low degrees of the superheat.