PROBLEM TO BE SOLVED: To provide a concentrator which has comparatively simple configuration and yet can sufficiently and securely prevent excess concentration of solution to be concentrated, and to provide a hydrogen peroxide gas generation apparatus with the concentrator.SOLUTION: The concentrator 20 includes: a container body 23 to store solution to be concentrated a heater 21a to heat the solution in the container body 23 a gas introduction port to blow the gas into a gas phase part of the container body 23 a gas exhaust port 25 provided in the gas phase part of the container body 23 a concentrated solution discharging means 26 for discharging the concentrated solution in the container body 23 and a temperature sensor 29 having a temperature detecting part 29a provided at a position which is exposed from a liquid level L when the liquid level L that is in the liquid phase at starting concentration of the solution and lowers with concentration of the solution reaches a level at which the concentration is to be stopped.
