An acceleration mechanism (50,51) comprising: an operating section; a working section; a base; a first spring that acts between the operating section and the working section; and a third spring that acts between the working section and the base, the operating section being moved from a first position to a second position by an external force, the working section being moved between a third position and a fourth position in response to a motion of the operating section between the first position and the second position, the first spring causing the working section to be moved by elastic energy stored by an external force that is applied to the operating section, in a case where the working section is in at least either the third position or the fourth position, a retention force that causes the working section to be retained in that position acting on the working section, wherein the third spring acts between the working section and the base such that a direction in which the force of the third spring is applied to the working section when the working section is in the third position is not parallel to a direction in which the force of the third spring is applied to the working section when the working section is in the fourth position, and the third spring acts between the working section and the base such that, during displacement of the working section from the third position to the fourth position, a component which, of the force of the third spring, acts in a direction of motion of the working section monotonically decreases, assuming that a direction of return of the working section from the fourth position to the third position is positive, wherein assuming that θ is an angle between a direction in which a connection point of the working section returns, the connection point being a point at which the third spring is connected to the working section, and a direction in which the force of the third spring is applied to the working section, cosθ is smaller when the working section is in the fourth position than when the working section is in the third position, characterised in that the angle θ is smaller than 90° when the working section is in the fourth position. an operating section; a working section; a base; a first spring that acts between the operating section and the working section; and a third spring that acts between the working section and the base, the operating section being moved from a first position to a second position by an external force, the working section being moved between a third position and a fourth position in response to a motion of the operating section between the first position and the second position, the first spring causing the working section to be moved by elastic energy stored by an external force that is applied to the operating section, in a case where the working section is in at least either the third position or the fourth position, a retention force that causes the working section to be retained in that position acting on the working section, wherein the third spring acts between the working section and the base such that a direction in which the force of the third spring is applied to the working section when the working section is in the third position is not parallel to a direction in which the force of the third spring is applied to the working section when the working section is in the fourth position, and the third spring acts between the working section and the base such that, during displacement of the working section from the third position to the fourth position, a component which, of the force of the third spring, acts in a direction of motion of the working section monotonically decreases, assuming that a direction of return of the working section from the fourth position to the third position is positive, wherein assuming that θ is an angle between a direction in which a connection point of the working section returns, the connection point being a point at which the third spring is connected to the working section, and a direction in which the force of the third spring is applied to the working section, cosθ is smaller when the working section is in the fourth position than when the working section is in the third position, characterised in that the angle θ is smaller than 90° when the working section is in the fourth position.