PURPOSE: To provide an injection timing adjustment device of a distributed type fuel injection pump, which occupies little space to be mounted, which does not generate fuel vapor at the time of pressure decrease in a high pressure chamber, without increasing the cost.

CONSTITUTION: A timer 11 is provided with a timer piston 13 that can slide in a pump housing 1, and with a servo valve 15 for controlling the movement of the timer piston 13 based on the rotational speed of a pump. A high pressure chamber 21 is formed out of an end surface of the timer piston 13, the pump housing 1, and of a surface plate 3, while a low pressure chamber 23 is formed out of the other end surface of the timer piston 13, the pump housing 1, and of a cover 5. A route 41 formed in the timer piston 13 is enlarged on the side part of an operational pin 29, and a filter 51 is provided therein. A route 53 for constantly communicating a route 41 to the high pressure chamber 21, is provided, while an orifice 55 is provided on the route 53.