To provide an electronic control device capable of preventing loss of data due to simultaneous generation of writing processing in a memory and a reset processing by a watchdog timer to improve reliability of data conserved in the memory.

This electronic control device 3 is provided with a microcomputer 10, a watchdog timer part 25 and a stand-by RAM 29. The watchdog timer part 25 includes a timer 28 to be cleared by a watchdog pulse from the microcomputer 10 and a reset processing part 27 for resetting the microcomputer 10 when a count value of the timer 28 reaches a reset threshold value VR. The electronic control device 3 is provided with a writing control means 24 for canceling writing in the stand-by RAM 29 when the count value of the timer 28 reaches a prescribed writing control threshold value VW and executing writing in the stand-by RAM 29 when the count value does not reach the threshold value VW, in relation to a writing request in the stand-by RAM 29.