A solar heat collecting system comprising: a heat collector including one or more heat collecting modules (1a, 1b, 1c) configured to heat a heat medium by a sunray; a heating device (4, 7) configured to heat a heat utilizing fluid by heat of the heat medium; and a heat medium flow path configured to circulate the heat medium between the heat collector and the heating device; characterized in that the system further comprising a controller configured to control circulation of the heat medium in the heat collector in accordance with an amount of direct solar radiation of the sunray, or in accordance with a temperature difference between a first temperature of the heat medium at a first position located in a vicinity of a heat medium entrance of one of the heat collecting modules and a second temperature of the heat medium at a second position located in a vicinity of a heat medium exit of one of the heat collecting module located downstream of the first position with respect to the heat medium, wherein the controller is configured to stop the circulation of the heat medium in all or part of the heat collector, when the amount of direct solar radiation is smaller than a predetermined value, when a time period in which the amount of direct solar radiation is smaller than the predetermined value lasts longer than predetermined time, when the temperature difference is smaller than a predetermined value, or when a time period in which the temperature difference is smaller than the predetermined value lasts longer than predetermined time, and the controller is configured to restart the circulation of the heat medium in the heat collector during the stop of the circulation of the heat medium in all or part of the heat collector, when the amount of direct solar radiation is larger than a predetermined value, when a time period in which the amount of direct solar radiation is larger than the predetermined value lasts longer than predetermined time, when the temperature difference is larger than a predetermined value, or when a time period in which the temperature difference is larger than the predetermined value lasts longer than predetermined time. a heat collector including one or more heat collecting modules (1a, 1b, 1c) configured to heat a heat medium by a sunray; a heating device (4, 7) configured to heat a heat utilizing fluid by heat of the heat medium; and a heat medium flow path configured to circulate the heat medium between the heat collector and the heating device; characterized in that the system further comprising a controller configured to control circulation of the heat medium in the heat collector in accordance with an amount of direct solar radiation of the sunray, or in accordance with a temperature difference between a first temperature of the heat medium at a first position located in a vicinity of a heat medium entrance of one of the heat collecting modules and a second temperature of the heat medium at a second position located in a vicinity of a heat medium exit of one of the heat collecting module located downstream of the first position with respect to the heat medium, wherein the controller is configured to stop the circulation of the heat medium in all or part of the heat collector, when the amount of direct solar radiation is smaller than a predetermined value, when a time period in which the amount of direct solar radiation is smaller than the predetermined value lasts longer than predetermined time, when the temperature difference is smaller than a predetermined value, or when a time period in which the temperature difference is smaller than the predetermined value lasts longer than predetermined time, and the controller is configured to restart the circulation of the heat medium in the heat collector during the stop of the circulation of the heat medium in all or part of the heat collector, when the amount of direct solar radiation is larger than a predetermined value, when a time period in which the amount of direct solar radiation is larger than the predetermined value lasts longer than predetermined time, when the temperature difference is larger than a predetermined value, or when a time period in which the temperature difference is larger than the predetermined value lasts longer than predetermined time.