PURPOSE: To improve the fitting workability of a spring brake device to a fitted body and easily attain the accuracy of the fitted body.

CONSTITUTION: A core 2 connected to an operating device, a pinion 4 interlocked with the rotation of the core 2, and a spring with the coil part brought into pressure contact with the inner surface of a bottomed cylindrical housing 1 opened on one side are rotatably enclosed in the housing 1 to form a spring brake device. Spring brake device fitting structure is formed of a holding plate 5 fixed to the opening side of the housing 1 and having a supporting part 5b for rotatably supporting a pinion shaft while covering a part of the opening and a plate like fitted body to which the housing 1 is fixed. This fitted body is provided with a hole bored in a size large enough to enable the supporting part 5b or the holding plate 5 to pass through to the opposite side from the fitting face side fitted to the housing 1.