Medicament delivery device comprising - an elongated housing (10, 10') having opposite distal and proximal ends, - a medicament container (18; 18') arranged inside said housing, - a medicament delivery member (16; 16') attachable to said medicament container; - a plunger rod (22; 22') arranged to act on a stopper (20; 20') inside said medicament container; - driving means arranged to interact with said plunger rod; and - an operation member (38; 38') transversally protruding through an elongated opening (39; 39') on the longitudinal surface of the elongated housing and interactively connected to the driving means for both setting and actuating the delivery of a dose of medicament characterised in that the driving means comprises: - a first elongated plate (36; 36') parallelly arranged in relation to the plunger rod and comprising the operation member (38; 38'); - a second elongated plate (40; 40') parallelly arranged in relation to the plunger rod and positioned generally opposite to the first elongated plate; - a lock member (48; 48') operatively connected to the plunger rod by first one-direction locking means such that the plunger rod can be linearly and proximally displaced but locked against a distally displacement; and - a linear movable driver (24; 24') operatively connected to both the first and the second elongated plates by gear means, and also operatively connected to the plunger rod by second one-direction locking means such that when said operation member is manually and distally displaced a certain distance corresponding to a set dose, said driver is also distally displaced in relation to said plunger rod and when said operation member is manually and proximally displaced, both the plunger rod and the driver which are locked to each other by the second one-direction locking means are also proximally displaced. - an elongated housing (10, 10') having opposite distal and proximal ends, - a medicament container (18; 18') arranged inside said housing, - a medicament delivery member (16; 16') attachable to said medicament container; - a plunger rod (22; 22') arranged to act on a stopper (20; 20') inside said medicament container; - driving means arranged to interact with said plunger rod; and - an operation member (38; 38') transversally protruding through an elongated opening (39; 39') on the longitudinal surface of the elongated housing and interactively connected to the driving means for both setting and actuating the delivery of a dose of medicament characterised in that the driving means comprises: - a first elongated plate (36; 36') parallelly arranged in relation to the plunger rod and comprising the operation member (38; 38'); - a second elongated plate (40; 40') parallelly arranged in relation to the plunger rod and positioned generally opposite to the first elongated plate; - a lock member (48; 48') operatively connected to the plunger rod by first one-direction locking means such that the plunger rod can be linearly and proximally displaced but locked against a distally displacement; and - a linear movable driver (24; 24') operatively connected to both the first and the second elongated plates by gear means, and also operatively connected to the plunger rod by second one-direction locking means such that when said operation member is manually and distally displaced a certain distance corresponding to a set dose, said driver is also distally displaced in relation to said plunger rod and when said operation member is manually and proximally displaced, both the plunger rod and the driver which are locked to each other by the second one-direction locking means are also proximally displaced.