To provide a transportable-type radiological image photographing apparatus which dispenses with the timing control for the irradiation timing of radiation and the read timing of image data, and which can prevent enlargement of the apparatus and will not narrow the flexibility of photographing, and to provide a radiological image photographing system that uses the apparatus.

The transportable-type radiological image photographing apparatus 1 includes radiation detecting elements 7 provided in two-dimensional shapes; a reading circuit 17 for reading the image data; an irradiation-detecting means 42 for detecting the start and termination of irradiation of radiation; a control means 22, which computes the image data of each radiation detecting element 7 from each image data read for each of frames, from the frame at which the irradiation of radiation is started to the frame next to the frame, at which the irradiation of radiation is terminated; and a reverse-bias power source 14, which applies a reverse-bias voltage on the radiation-detecting element 7 via a bias line 9. The irradiation-detecting means 42 detects the start and termination of the irradiation of radiation, based on the increase and decrease in the current flowing through the bias line 9.