A collision detecting device includes a chamber member providing a space, a pressure sensor for detecting a pressure inside the space, a determination means, a bumper absorber for absorbing an impact generated by collision and a temperature sensor for detecting a temperature of the chamber member. Hardness of the chamber member changes with temperature. Thus, the deformation degree of the chamber member is different depending on temperature. However, the determination means corrects the pressure detected by the pressure sensor based on the temperature detected by the temperature sensor, and determines collision based on the corrected pressure. Therefore, a collision detecting device which can determine collision of an object with a vehicle accurately without being affected by the change of temperature can be obtained.